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General Definitions


Abducens nerve or Cranial nerve VI
The motor nerve innervating the lateral rectus muscle, which abducts the eye; lesions of the nucleus, which is located in the dorsal pons, produce a horizontal gaze palsy; nerve fibers exit the ventromedial pons and because of their long course are vulnerable to damage by mass lesions/increased intracranial pressure.

Anatomic Orientation - The motion of a body part away from the midline of the body.

Abductor muscle
A muscle used to pull a body part away from the midline of the body (e.g., the abductor leg muscles are used to spread the legs).

The loss of will, impulse, and decision-making ability.

Action potential
An electrical charge that travels along the axon to the neuron's terminal, where it triggers the release of a neurotransmitter. This occurs when a neuron is activated and temporarily reverses the electrical state of its interior membrane from negative to positive.

Acquired immune deficiency syndrome (AIDS)
Acquired immune deficiency syndrome (AIDS) is the last stage of human immunodeficiency virus (HIV) disease, a viral disease that slowly destroys the body's immune system. AIDS is typically diagnosed when a person's number of immune system CD4 cells, or T-cells, drops below 200. When a person is diagnosed with AIDS, he or she also has become affected by diseases and conditions, possibly including cancer, which may attack the body in the absence of a strong, uncompromised immune system.

Acquired immunity
An immunity that develops with exposure to various antigens. Your immune system builds a defense that is specific to that antigen.

Clarity of vision. Visual acuity is expressed as a fraction of normal vision. 20/400 means an eye that sees at 20 feet what an average eye sees at 400 feet.

ACTH (Adrenocorticotropic hormone)
ACTH is extracted from the pituitary glands of animals or made synthetically. ACTH stimulates the adrenal glands to release glucocorticoid hormones. These hormones are anti-inflammatory in nature, reducing edema and other aspects of inflammation. Data from the early 1970s indicate that ACTH may reduce the duration of MS exacerbations. In recent years it has been determined that synthetically produced glucocorticoid hormones (e.g., cortisone, prednisone, prednisolone, methylprednisolone, betamethasone, dexamethasone), which can be directly administered without the use of ACTH, are more potent, cause less sodium retention and less potassium loss, and are longer-acting than ACTH.

Activities of daily living (ADLs)
Activities of daily living include any daily activity a person performs for self-care (feeding, grooming, bathing, dressing), work, homemaking, and leisure. The ability to perform ADLs is often used as a measure of ability/disability in MS.

A rapid onset usually with a recovery, not chronic or long-lasting.

Acute Disseminated Encephalomyelitis (ADEM)
ADEM is a brief but widespread bout of inflammation that can damage myelin in your brain , spinal cord, and sometimes the optic nerve. Typically the condition occurs when your body attacks its own tissues in response to infection with a virus or bacteria. Less likely it is because of a reaction to a vaccine. Sometimes the cause cannot be determined. Children get ADEM more often than adults do. Symptoms usually come on quickly and may include: Fever, low energy, headache, nausea and vomiting, confusion, irritation, eyesight problems, and trouble with coordination.

Adaptive immune response
This is characterized by antigen-specific reactions through T and B lymphocytes. It has memory and subsequent antigen exposure is met with more vigorous and rapid responses.

Anatomic Orientation - The motion of a body part toward the midline of the body.

Adductor muscle
A muscle that pulls inward toward the midline of the body (e.g., the adductor leg muscles are used to pull the legs together).

(See: Acute Disseminated Encephalomyelitis)

The four basic stages of a medicine's life in the body are absorption, distribution, metabolism, and excretion or ADME.

Adverse reaction or event
An unwanted effect caused by the administration of drugs. Onset may be sudden or develop over time.
(See: Side effects)

Advocacy and support groups
Organizations and groups that actively support participants and their families with valuable resources, including self-empowerment and survival tools.

Affective release
Also called pseudo-bulbar affect or pathological laughing and weeping; a condition in which episodes of laughing and/or crying occur with no apparent precipitating event. The person's actual mood may be unrelated to the emotion being expressed. This condition is thought to be caused by lesions in the limbic system, a group of brain structures involved in emotional feeling and expression.

Afferent neurons
These neurons convey information from tissues and organs into the CNS. Also called sensory neurons.

Afferent pupillary defect
An abnormal reflex response to light that is a sign of nerve fiber damage due to optic neuritis. A pupil normally gets smaller when a light is shined either into that eye (direct response) or the other eye (indirect response). In an afferent pupillary defect, also called Marcus Gunn pupil, there is a relative decrease in the direct response. This is most clearly demonstrated by the "swinging flashlight test." When the flashlight is shined first in the abnormal eye, then in the healthy eye, and then again in the eye with the pupillary defect, the affected pupil becomes larger rather than smaller.

A molecule that triggers a cellular response by interacting with a receptor.

This is the inability to initiate movement due to difficulty selecting and/or activating motor programs in the central nervous system, often described as "freezing in place." This can take the form of full temporary paralysis, or mean that the person can only move slowly or with extreme difficulty.

An substance that induces an allergic state or reaction.

Alternative medicine
An unconventional therapy used instead of conventional medicines. Any therapy that is not standard, including herbal medicines, acupuncture, and acupressure, as well as medicinal therapies, such as shark cartilage, maitake mushroom, etc.

Alzheimer's disease
A major cause of dementia in the elderly, this neurodegenerative disorder is characterized by the death of neurons in the hippocampus, cerebral cortex, and other brain regions.

The brains limbic structure involved in many functions, including emotion, learning and memory. It's part of a system that processes "reflexive" emotions like fear and anxiety.

Amyotrophic lateral sclerosis (ALS)
A degenerative disorder affecting the motor neuron cells and the motor tracts in the brain and spinal cord; also known as Lou Gehrig's disease.

Complete numbness/loss of sensation.

A substance that relieves pain.

Anaphylactoid reactions
Anaphylactoid reactions have symptoms similar to those of anaphylaxis, but are triggered instead by non-IgE mechanisms which directly cause the release of these mediators.

An immediate and short-lived, usually severe reaction in which the body responds to what is perceived to be a foreign substance with exaggerated symptoms, such as extreme itching, swelling, and often life-threatening respiratory distress.

The technique of mechanically widening a narrowed or obstructed blood vessel.

Annulus fibrosus
The outer, fibrous, ring-like portion of an intervertebral disc.

Anatomic Orientation - Referring to the front of the body. Opposite of posterior.

Anatomic Orientation - Situated or occurring in front of and to the side.

Anatomic Orientation - From front to back, as opposed to posteroanterior.

Proteins produced in a controlled manner by certain white blood cells (lymphocytes) to neutralize an antigen or foreign protein and fight disease, but whose uncontrolled production can cause illness; immunoglobulin. They are produced in reaction to foreign antigens, bacteria, or viruses.

Refers to the action of certain medications commonly used in the management of neurogenic bladder dysfunction. These medications inhibit the transmission of parasympathetic nerve impulses and thereby reduce spasms of smooth muscle in the bladder.

A drug's ability to reduce inflammation, which can cause soreness and swelling.

A substance that triggers the immune system to produce antibodies (an immune response), resulting in production of an antibody as part of the body's defense against an infection, disease, or allergen.

Antinuclear antibodies (ANA)
The amount and pattern of antibodies in your blood that work against your own body (autoimmune reaction). In autoimmune diseases, the immune system attacks and destroys the body's normal tissues. When a person has an autoimmune disease, the immune system produces antibodies that attach to the body's own cells as though they were foreign substances, often causing them to be damaged or destroyed.

Antinuclear antibody (ANA) test
This measures the amount and pattern of antibodies in your blood that work against your own body (autoimmune reaction).

The difficulty understanding the speech of other people and/or expressing oneself verbally. Occurs in the production or comprehension of language.

Approved drugs
In the U.S., the Food and Drug Administration (FDA) must approve a substance as a drug before it can be marketed. The approval process involves several steps including pre-clinical laboratory and animal studies, clinical trials for safety and efficacy, filing of a New Drug Application by the manufacturer of the drug, FDA review of the application, and FDA approval/rejection of application.

Inflammation of the arachnoid membrane or the middle of the three protective layers called the meninges, most commonly seen around the spinal cord and cauda equina.

Inflammation of a joint, usually accompanied by swelling, pain, and restriction of motion.

Inhalation of food particles or fluids into lungs.

Assistive devices
Any tools that are designed, fabricated, and/or adapted to assist a person in performing a particular task, (e.g., cane, walker, shower chair).

Assistive technology
A term used to describe all of the tools, products, and devices, from the simplest to the most complex, that can make a particular function easier or possible to perform.

Astrocytes, also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical support of endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and have a role in the repair and scarring process of the brain and spinal cord following traumatic injuries.

Astrogliosis or Astrocytosis is an abnormal increase in the number of astrocytes due to the destruction of nearby neurons.

Loss of coordination or unsteadiness of the body's posture or limb movement and/or strength due to disease activity in the cerebellum or nerves connecting to it. Ataxia is most often caused by disease activity in the cerebellum.

Ataxia telangiectasia (AT)
A progressive, degenerative genetic disease, which causes degeneration of the nervous system, cancer, and immunodeficiency.

A wasting away or decrease in size of a cell, tissue, or organ of the body because of disease or lack of use.

(See: Exacerbation)

Autoimmune disease
Disease where the body's immune system causes itself to attack healthy cells, organs, or tissues.

Autonomic nervous system
The part of the nervous system that controls involuntary functions such as the heart, smooth muscles, glands, and intestinal activity.

The extension of a nerve cell that then passes an impulse on to the next cell or muscle. Axons are generally smaller than 1 micron (1 micron = 1/1,000,000 of a meter) in diameter, but can be as much as a half meter in length.

Pertaining to the axon.

Axonal damage
Injury to the axon in the nervous system, generally as a consequence of trauma or disease. This damage may involve temporary, reversible effects or permanent severing of the axon. Axonal damage usually results in short-term changes in nervous system activity, or permanent inability of nerve fibers to send their signals from one part of the nervous system to another or from nerve fibers to muscles. The damage can thus result in a variety of symptoms relating to sensory or motor function.

Axonal degeneration
A type of peripheral nerve fiber response to insult, wherein axon death and subsequent breakdown occur, with secondary breakdown of the myelin sheath associated. Caused by focal injury to peripheral nerve fibers and referred to as Wallerian degeneration.

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B cell or lymphocyte
A type of lymphocyte or white blood cell that is manufactured in the bone marrow that makes antibodies.

Babinski reflex
A neurologic sign in MS in which stroking the outside sole of the foot with a pointed object causes an upward (extensor) movement of the big toe rather than the normal (flexor) bunching and downward movement of the toes.

Basal ganglia
A series of structures located deep in the brain that are responsible for motor movements.

A white blood cell that releases histamine (a substance involved in allergic reactions) and that produces substances to attract other white blood cells (neutrophils and eosinophils) to a trouble spot.

Bell's Palsy
Paralysis of the facial nerve caused by MS, a viral infection, or other infections.

Benign MS
Initial attack followed by little or no progression.

Benign paroxysmal positional vertigo (BPPV)
It is a disorder caused by problems in the inner ear. Its symptoms are repeated episodes of positional vertigo, that is, of a spinning sensation caused by changes in the position of the head.

Anatomic Orientation - Relating to, or affecting both sides of the body.

Biological response modifiers (BRMs)
Substances that stimulate the body's response to infection and disease. The body naturally produces small amounts of these substances. Scientists can produce some of them in the laboratory in large amounts.

Biologic therapy
A systemic therapy utilizing interferon or interleukin.

Chemical alteration of a substance within the body, as by the action of enzymes.

Black hole artifact
With multiple sclerosis (MS), a T1-weighted magnetic resonance imaging (MRI) scan shows black holes, which are areas of permanent axonal damage. These are called hypointense lesions, meaning that they display as dark areas on the MRI image. T1-weighted lesions can also be areas of edema or swelling, which are not permanent and disappear on subsequent scans.

Blood-brain barrier
A semi permeable cell layer around the blood vessels in the CNS that keeps immune cells, foreign bodies and viruses out.

In regards to the immune system, it's where immune cells constantly circulate throughout the bloodstream, patrolling for problems. When blood tests are used to monitor white blood cells, another term for immune cells, a snapshot of the immune system is taken. If a cell type is either scarce or overabundant in the bloodstream, this may reflect a problem.

Bone Marrow
The bone marrow contains stems cells that can develop into a variety of cell types. The common myeloid progenitor stem cell in the bone marrow is the precursor to innate immune cells—neutrophils, eosinophils, basophils, mast cells, monocytes, dendritic cells, and macrophages—that are important first-line responders to infection.

Bone spur
Bony growth or rough edge of bone.

A slowing of motor movements due to dysfunction of the basal ganglia and related structures.

That part of the central nervous system that is contained within the cranium or skull.

Brain injury
(1) Closed head injury (CHI), which is caused by rapid acceleration and deceleration of the head during which the brain bounces off the inside of the skull;
(2) Open head injury (OHI), caused by car accident, gunshot wound, or other external factor.

The part of the central nervous system that houses the nerve centers of the head as well as the centers for respiration and heart control. It extends from the base of the brain to the spinal cord.

Brainstem auditory evoked potential (BAEP)
A test in which the brain's electrical activity in response to auditory stimuli (like clicking sounds) is recorded by an electroencephalograph and analyzed by computer. Demyelination results in a slowing of response time. This test is sometimes useful in the diagnosis of MS because it can confirm the presence of a suspected lesion or identify the presence of an unsuspected lesion that has produced no symptoms. BAEPs have been shown to be less useful in the diagnosis of MS than either visual or somatosensory evoked potentials.

Brownian motion
Also called Pedesis, this is the seemingly random movement of particles suspended in a fluid (like a liquid such as water or a gas such as air) or the mathematical model used to describe such random movements, often called a particle theory.

Burden of disease
The total estimated area in mm2 or volume in mm3 of hyperintense lesions identified on PD/T2-MRI scans.
(See: Total lesion load)

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Cauda equina
The collection of nerves at the end of the spinal cord that resembles a horse’s tail.

Caspases or cysteine-aspartic acid proteases play essential roles in apoptosis (programmed cell death), necrosis and inflammation.

Anatomic Orientation - Toward the feet or tail in embryology, as opposed to cranial.

Anatomic Orientation - Pertaining to, situated in, or toward the tail or the hind part or below another structure.

CT or CAT scan
(See: Computerized axial tomography)

The smallest unit of a living organism, composed of a nucleus and cytoplasm surrounded by a membrane.

Central nervous system (CNS)
The brain, spinal cord, and optic nerves.

Central pain syndrome (CPS)
This is a neurological condition caused by damage to the central nervous system (CNS). It may occur in patients who have experienced spinal cord injury, brain injury, or stroke and in patients with multiple sclerosis (MS). It's characterized by steady pain (usually described as a burning, aching, or cutting sensation) and brief bursts of sharp pain. Central pain syndrome may develop years after damage to the CNS occurs.

Centrocecal scotoma
A blind spot or localized defect in the visual field bordered by an area of normal vision.

The large, upper part of the brain that acts as a master control system and is responsible for initiating thought and motor activity. Its two hemispheres, united by the corpus callosum, form the largest part of the central nervous system.

Located at the lower back of the head and connected to the brain stem, it's the second largest structure of the brain and is made up of two hemispheres. The cerebellum controls complex motor functions such as walking, balance, posture, and general motor coordination.

Cerebral cortex
The outermost layer of the cerebral hemispheres of the brain. It's largely responsible for all forms of conscious experience, including perception, emotion, thought, and planning.

Cerebrospinal fluid (CSF)
Clear fluid in the ventricles and surrounding the brain and surrounding the spinal cord. It provides nutrients and serves to cushion the brain and therefore protect it from injury. As this fluid gets absorbed, more is produced from the choroid plexus, a structure located in the ventricles.

The main portion of the brain in the upper part of the cranial cavity and is divided into two hemispheres joined by the corpus callosum.

Cervical spine
The neck region of the spine, which consists of the first seven vertebrae.

Charcot-Marie-Tooth disease
A progressive debilitating neuromuscular disorder; also hereditary motor sensory neuropathy and peroneal muscular atrophy.

These are very small cytokines with substantial chemotactic function important for directing movement or migration of circulating leukocytes to sites of inflammation or injury.

The process of using a chemical substance to attract cells to a particular site.

A chromosome is an organized structure of DNA and protein that is found in cells.
(See: Genetic Definitions: Chromosome)

For a long duration typically to describe a disease that has gradual worsening.

Chronic Cerebrospinal Venous Insufficiency (CCSVI)
Describes the compromised flow of blood in the veins draining the central nervous system.

Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)
A neurological disorder that targets your body's nerves causing inflammation of nerves and nerve roots. The swelling can damage and/or destroy the myelin which will slow the nerves' ability to send signals. This is what causes the weakness, pain, fatigue, and numbness. It is closely related to Guillain-Barré syndrome (GBS) but GBS usually comes on days or weeks after a person has an illness, such as a stomach bug and once treated, most people recover fairly quickly. CIDP isn’t linked to illness and tends to be a longer-term problem. In rare cases, people who don’t recover from GBS may develop CIDP.

Chronic-Progressive MS (CPMS)
(note: outdated and no longer used as of 2013)
An almost continual progression of symptoms.

Cingulate gyrus
Portion of the brain that plays a role in processing conscious emotional experience.

Circle of Willis
A circle of arteries at the base of the brain that is fed by the two paired internal carotid arteries and the two paired vertebral arteries.

The swinging of the leg out to the side.

Pertaining to or founded on observation and treatment of participants, as distinguished from theoretical or basic science.

Clinical findings
Observations made during a medical exam indicating a change or impairment in mental or physical functions.

Clinically isolated syndrome (CIS)
A first neurologic event that is suggestive of demyelination, accompanied by multiple, clinically "silent" (asymptomatic) lesions on MRI that are typical of MS. Individuals with this syndrome are at high risk for developing clinically definite MS.

Closed-eye visualization
(See: Phosphenes)

A sign of spasticity in which involuntary shaking or jerking of the leg occurs when the toe is placed on the floor with the knee slightly bent. The shaking is caused by repeated, rhythmic, reflex muscle contractions.

The Consolidated Omnibus Budget Reconciliation Act (COBRA) gives workers and their families who lose their health benefits the right to choose to continue group health benefits provided by their group health plan for limited periods of time under certain circumstances such as voluntary or involuntary job loss, reduction in the hours worked, transition between jobs, death, divorce, and other life events. Qualified individuals may be required to pay the entire premium for coverage up to 102 percent of the cost to the plan.

More commonly known as the tailbone, this is a bony structure in the region of the spine below the sacrum.

High level functions carried out by the human brain, including comprehension and use of speech, visual perception and construction, calculation ability, attention (information processing), memory, and executive functions such as planning, problem-solving, and self-monitoring.

Cognitive deficit
This is an inclusive term to describe any characteristic that acts as a barrier to cognitive performance. Cognitive deficits may be congenital or caused by environmental factors such as brain injuries, neurological disorders (such as MS), or mental illness.

Cognitive difficulties
Cognitive difficulties are problems with cognitive functioning, which include the intellectual activities of thinking, reasoning, remembering, imagining, or learning words.

Cognitive impairment
Changes in cognitive function from trauma or disease including memory and information processing. Some degree of cognitive impairment occurs in approximately 50–60 percent of people with MS, with memory, information processing, and executive functions being the most commonly affected functions.

Cognitive rehabilitation
Techniques designed to improve the functioning of individuals whose cognition is impaired because of physical trauma or disease. Rehabilitation strategies are designed to improve the impaired function through repetitive drills or practice, or to compensate for impaired functions that are not likely to improve. Cognitive rehabilitation is provided by psychologists and neuropsychologists, speech/language pathologists, and occupational therapists.

Cognitive reserve
This describes the mind's resilience to neuropathological damage of the brain.

In epidemiology, a group of individuals with some characteristics in common.

Combined (bladder) dysfunction
A type of neurogenic bladder dysfunction in MS (also called detrusor-external sphincter dyssynergia—DESD). Simultaneous contractions of the bladder’s detrusor muscle and external sphincter cause urine to be trapped in the bladder, resulting in symptoms of urinary urgency, hesitancy, dribbling, and incontinence.

Compassionate use
A method of providing experimental therapeutics prior to final FDA approval for use in humans. This procedure is used with very sick individuals who have no other treatment options. Often, case-by-case approval must be obtained from the FDA for "compassionate use" of a drug or therapy.

Complement system
A group of proteins that are involved in a series of reactions (cascade) designed to defend the body and that have various immune functions, such as killing bacteria and other foreign cells, making foreign cells easier for macrophages to identify and ingest, attracting macrophages and neutrophils to a trouble spot, and enhancing the effectiveness of antibodies.

Complementary medicine
An unconventional therapy used in combination with conventional medicine.

Computerized axial tomography (CT or CAT scan)
A non-invasive diagnostic radiology technique for examining soft tissues of the body. A computer integrates X-ray scanned "slices" of the organ being examined into a cross-sectional picture.

Occurring during the same time period as in taking two or more medications. Can also refer to secondary symptoms that occur with a main symptom.

Conduction block
A failure of generation of an action potential at the nodes of Ranvier due to the loss of myelin in the paranodal region may result in slowing or failure of conduction through a nerve segment. Weakness, numbness and other 'negative' symptoms of MS can be attributed either to blocked conduction or to critical loss of axons in a pathway.

A shortening of muscle fibers that results in the movement of a joint.

A permanent shortening of the muscles and tendons adjacent to a joint, which can result from severe, untreated spasticity and interferes with normal movement around the affected joint. If left untreated, the affected joint can become frozen in a flexed or bent position.

A specific circumstance when the use of certain treatments could be harmful.

Conus medullaris
The cone-shaped bottom of the spinal cord.

An organized working together of muscles and groups of muscles aimed at bringing about a purposeful movement such as walking or standing.

Corpus callosum
It is the largest white matter tract connecting the two cerebral hemispheres that plays an important role in the performance of complex tasks requiring precise timing of information transfer between multiple brain regions. Atrophy here is common in MS and correlates with cognitive impairment and, reduced speed and accuracy on information processing tasks. Abnormalities here may be focal plaques or atrophy. Hyper-intensity of its undersurface (also termed the callosal-septal interface) on a midsagittal (long TR/short TE spin echo) image has been considered a relatively specific indicator of MS. The detection on FLAIR images of earlier, subtle findings, such as subcallosal striations, may be an aid to early diagnosis.

Any of the natural or synthetic hormones associated with the adrenal cortex (which influences or controls many body processes). Corticosteroids include glucocorticoids, which have an anti-inflammatory and immunosuppressive role in the treatment of MS exacerbations.

A glucocorticoid steroid hormone, produced by the adrenal glands or synthetically, that has anti-inflammatory and immune-system suppressing properties. Prednisone and prednisolone also belong to this group of substances.

Anatomic Orientation - Toward the head, as opposed to caudad.

Cranial nerves
The nerves that carry sensory, motor, or parasympathetic fibers to the face and neck, included are the optic nerve, oculomotor nerve, facial nerve, trigeminal nerve, auditory nerve, and vagus nerve.

Crohn’s disease
Crohn’s disease is a disorder that causes parts of the digestive tract to become inflamed and swell. Crohn’s most commonly affects the lower small intestine, or the ileum, but it can affect any portion of the digestive tract. The most common symptoms of Crohn’s disease are diarrhea and abdominal pain.

Cutaneous sense
The skin senses including touch, pressure, pain, heat and cold.

Messenger chemical proteins produced by various cells, particularly those of the immune system, to influence the activity of other cells and help regulate an immune response.

Cytotoxic drug
A drug that kills cells such as chemotherapy.

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An ulcer (sore) of the skin resulting from pressure and lack of movement such as occurs when a person is bed- or wheelchair-bound. The ulcers occur most frequently in areas where the bone lies directly under the skin, such as elbow, hip, or over the coccyx (tailbone). A decubitus ulcer may become infected and cause general worsening of the person’s health.

Anatomic Orientation - Away from the exterior surface or further into the body, as opposed to superficial.

Deep tendon reflexes
The involuntary jerks that are normally produced at certain spots on a limb when the tendons are tapped with a hammer. Reflexes are tested as part of the standard neurologic exam.

A generally profound and progressive loss of intellectual function, sometimes associated with personality change that results from loss of brain substance and is sufficient to interfere with a person’s normal functional activities.

A loss of myelin in the white matter of the central nervous system (CNS).

A short arm-like protuberance from a nerve cell or neuron. Dendrites from neurons next to one another are tipped by synapses, tiny transmitters and receivers for chemical messages between the cells.

Dendritic cell
A cell that is derived from white blood cells, resides in tissues, and helps T cells recognize foreign antigens.

Densities on plain x-rays vary from black to white, depending on the composition of the material the x-rays pass through; black indicates the lowest x-ray density (air) and white, the highest (bone).

Deoxyribonucleic Acid (DNA)
(See: Genetic Definitions: DNA)

A mental disorder characterized by sadness, hopelessness, pessimism, loss of interest in life, reduced emotional well-being, and abnormalities in sleep, appetite, and energy level.

Detrusor muscle
A muscle of the urinary bladder that contracts and causes the bladder to empty.

Diffusion MRI
This is a magnetic resonance imaging (MRI) method that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion.

Diffusion tensor imaging (DTI)
A diffusion MRI method that is important when a tissue such as the neural axons of white matter in the brain has an internal fibrous structure. Water will then diffuse more rapidly in the direction aligned with the internal structure, and more slowly as it moves perpendicular to the preferred direction.

Diffusion weighted imaging (DWI)
A diffusion MRI method where each image voxel (three dimensional pixel) has an image intensity that reflects a single best measurement of the rate of water diffusion at that location. This measurement is more sensitive to early changes than more traditional MRI measurements such as T1 or T2 relaxation rates. DWI is most applicable when the tissue of interest is dominated by isotropic water movement such as gray matter in the cerebral cortex and major brain nuclei.

Double vision, or the simultaneous awareness of two images of the same object that results from a failure of the two eyes to work in a coordinated fashion. Covering one eye will erase one of the images.

As defined by the World Health Organization, a disability (resulting from an impairment) is a restriction or lack of ability to perform an activity in the manner or within the range considered normal for a human being.

A tough, elastic cushion located between the vertebra in the spinal column; acts as a shock absorber for the vertebra.

Disc degeneration
Degeneration or wearing out of a disc. A disc in the spine may deteriorate or wear out over time. A deteriorated disc may or may not cause pain.

Disease burden
This is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators. It's often quantified in terms of quality-adjusted life years (QALYs) or disability-adjusted life years (DALYs), which combine the burden due to both death and morbidity into one index. This allows for the comparison of the disease burden due to various risk factors or diseases. It also makes it possible to predict the possible impact of health interventions.

Disease-modifying therapy or drug (DMT)
A drug that reduces the frequency of clinical attacks.

In medicine, a disorder is a functional abnormality or disturbance. Medical disorders can be categorized into mental disorders, physical disorders, genetic disorders, emotional and behavioral disorders, and functional disorders.

Anatomic Orientation - Located farther away or downstream.

(See: Disease-modifying therapy)

DNA (Deoxyribonucleic Acid)
(See: Genetic Definitions: DNA)

Anatomic Orientation - Relating to the back or posterior of a structure. As opposed to the ventral, or front, of the structure. Some of the dorsal surfaces of the body are the back, buttocks, calves, and the knuckle side of the hand.

Drug-drug interaction
A modification of the effect of a drug when administered with another drug. The effect may be an increase or a decrease in the action of either substance, or it may be an adverse effect that is not normally associated with either drug.

The pattern of physiological response to varied dosage of a drug in which there is typically little or no effect at very low dosages and a toxic or unchanging effect at high dosages.
Poorly articulated or slurred speech due to damage on the nerves controlling the muscles controlling speech.

Disorder of color vision.

Impairment of the ability to make rapid alternating movements of motion that is caused by cerebellar dysfunction.

Distorted sensations felt when skin is touched usually caused by damage to the sensory pathways.

Loss of coordination from lesions in the cerebellum in which the ability to control the distance, power, and speed of an act is impaired.

Difficulty in swallowing that could cause food or saliva to enter the airway.

The difficulty understanding or using language.

Disorders of voice quality (including poor pitch control, hoarseness, breathiness, and hypernasality) caused by spasticity, weakness, and incoordination of muscles in the mouth and throat.

Air starvation with pained breathing. It occurs normally from physical exertion, and abnormally either from impaired respiration, emotional distress, or a breakdown in nerve responses.

This is impaired or disordered muscle tone that causes slow movement or an extended, sustained spasm in a group of muscles. Movements are often involuntary, twisting, writhing and repetitive.

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Localized or systemic condition in which the body tissues contain an excessive amount of fluid. Often found in plaque or scars where myelin has been destroyed.

Efferent neurons
These neurons transmit signals from the CNS to effector cells. Sometimes called motor neurons.

Efficacy of a drug or treatment
The maximum ability of a drug or treatment to produce a result regardless of dosage. A drug passes efficacy trials if it is effective at the dose tested and against the illness for which it is prescribed.

Electroencephalography (EEG)
A diagnostic procedure that records, via electrodes attached to various areas of the person's head, electrical activity generated by brain cells.

Electromyography (EMG)
Test for the peripheral nerves to conduct impulses to muscles using a needle or electrode to detect.

Based on experimental data, not on a theory.

An inflammation or infection of the brain.

A disorder or disease of the brain.

Overall outcome that the protocol is designed to evaluate. Common endpoints are severe toxicity, disease progression, or death.

A molecule (usually a protein) that speeds up, or catalyzes, a chemical reaction without being permanently altered or consumed.

A white blood cell that kills bacteria, that kills other foreign cells too big to ingest, that may help immobilize and kill parasites, that participates in allergic reactions, and that helps destroy cancer cells.

The study of disease patterns such as geography, genetics, demographics, and socioeconomic status in a population. The study of incidence and distribution and control of a disease in a population.

Epstein-Barr Virus (EBV)
The Epstein-Barr Virus, also called Human Herpes virus 4 (HHV-4), is a virus of the herpes family and is one of the most common viruses in humans. Most people become infected with EBV, which is often asymptomatic but commonly causes infectious mononucleosis.

Equilibrioception or sense of balance is one of the physiological senses. Broadly defined, a sense is a mechanism or faculty by which a living organism receives information about its external or internal environment, allowing it to react accordingly. The sense of balance reflects an awareness of equilibrium involving the perception of gravity. It helps prevent falling over when walking or standing still. Equilibrioception is determined by the level of fluid (called endolymph) in the labyrinth—a complex set of tubing in the inner ear.

The study of all factors that may be involved in the development of a disease, including the patient's susceptibility, the nature of the disease-causing agent, and the way in which the person's body is invaded by the agent.

A state of intense happiness and feelings of well-being.

The motion of a body part as it tilts away from the midline.

Evoked potentials (EPs)
EPs are recordings of the nervous system’s electrical response to the stimulation of specific sensory pathways (e.g., visual, auditory, general sensory). In tests of evoked potentials, a person’s recorded responses are displayed on an oscilloscope and analyzed on a computer that allows comparison with normal response times. Demyelination results in a slowing of response time. EPs can demonstrate lesions along specific nerve pathways whether or not the lesions are producing symptoms, thus making this test useful in confirming the diagnosis of MS. Visual evoked potentials are considered the most useful in MS.

The worsening of symptoms, appearance of new symptoms or the aggravation of old ones, lasting at least twenty-four hours (synonymous with attack, relapse, flare-up, or worsening), and usually associated with inflammation and demyelination in the brain or spinal cord.

Expanded Disability Status Scale (EDSS)
A part of the Minimal Record of Disability that summarizes the neurologic examination and provides a measure of overall disability. The EDSS is a 20-point scale, ranging from 0 (normal examination) to 10 (death due to MS) by half-points. A person with a score of 4.5 can walk three blocks without stopping; a score of 6.0 means that a cane or a leg brace is needed to walk one block; a score over 7.5 indicates that a person cannot take more than a few steps, even with crutches or help from another person. The EDSS is used for many reasons, including deciding future medical treatment, establishing rehabilitation goals, choosing subjects for participation in clinical trials, and measuring treatment outcomes. This is currently the most widely used scale in clinical trials.

Experimental allergic encephalomyelitis (EAE)
Experimental allergic encephalomyelitis is an autoimmune disease resembling MS that has been induced in some genetically susceptible research animals. Before testing on humans, a potential treatment for MS may first be tested on laboratory animals with EAE in order to determine the treatment’s efficacy and safety.

Experimental drug
A drug that is not FDA licensed for use in humans, or as a treatment for a particular condition.
(See: Off-label use)

Extensor spasm
A symptom of spasticity in which the legs straighten suddenly into a stiff, extended position. These spasms, which typically last for several minutes, occur most commonly in bed at night or on rising from bed.

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A posterior structure of a vertebra which articulates (joins) with a facet of an adjacent vertebra to form a facet joint that allows motion in the spinal column. Each vertebra has a right and left superior (upper) facet and a right and left inferior (lower) facet.

Familial aggregation
Occurrence of a trait in more members of a family than can be readily accounted for by chance.

A lessened capacity to do things along with feeling tired or worn out.

Finger-to-nose test
As a test of dysmetria and intention tremor, the person is asked, with eyes closed, to touch the tip of the nose with the tip of the index finger. This test is part of the standard neurologic exam.

A decrease in muscle tone resulting in weakened muscles and therefore loose, "floppy" limbs.

(See: Fluid attenuated inversion recovery)

(See: Exacerbation)

Flexor spasm
Involuntary, sometimes painful contractions of the flexor muscles, which pull the legs upward into a clenched position. These spasms, which last two to three seconds, are symptoms of spasticity. They often occur during sleep, but can also occur when the person is in a seated position.

Optic floaters can take many forms from little dots, circles, lines, to clouds or cobwebs. Sometimes people experience one large floater which can be distracting and make things difficult to read while others experience many floaters.

Fluid attenuated inversion recovery (FLAIR)
A pulse sequence used in magnetic resonance imaging (MRI) where the pulse sequence is an inversion recovery technique that nulls fluids. Lesions that are normally covered by bright fluid signals using conventional T2 contrast are made visible by the dark fluid technique. Flair is similar to T2 except the signal from cerebrospinal fluid (CSF) is suppressed so lesions will not be confused with fluids from CSF which also appears bright.

Food and Drug Administration (FDA)
FDA is an agency within the U.S. Department of Health and Human Services that is responsible for protecting the public health by assuring the safety, efficacy, and security of human and veterinary drugs, biological products, medical devices, our nation’s food supply, cosmetics, and products that emit radiation. The FDA is also responsible for advancing the public health by helping to speed innovations that make medicines and foods more effective, safer, and more affordable; and helping the public get the accurate, science-based information they need to use medicines and foods to improve their health. Pertaining to this website, it's responsible for enforcing governmental regulations pertaining to the manufacture and sale of drugs and to prevent the sale of impure or dangerous substances. Any new drug that is proposed for the treatment of MS in the U.S. must be approved by the FDA.

Foot drop
A condition of weakness in the muscles of the foot and ankle, caused by poor nerve conduction, which interferes with a person’s ability to flex the ankle and walk with a normal heel-toe pattern. The toes touch the ground before the heel, causing the person to trip or lose balance.

A normally occurring opening or passage in the vertebrae of the spine through which the spinal nerve roots travel.

An arch-like structure of the brain that connects the hippocampus to other parts of the limbic system.

Fourier transform
In mathematics, the Fourier transform (FT) is an operation that transforms one complex-valued function of a real variable into another. In such applications as signal processing, the domain of the original function is typically time and is accordingly called the time domain. The domain of the new function is typically called the frequency domain, and the new function itself is called the frequency domain representation of the original function. It describes which frequencies are present in the original function.

Frontal lobes
The largest lobes of the brain. The anterior or front part of each of the cerebral hemispheres that make up the cerebrum. The back part of the frontal lobe is the motor cortex, which controls voluntary movement; the area of the frontal lobe that is further forward is concerned with learning, behavior, judgment, and personality.

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A chemical compound that is used during magnetic resonance imaging (MRI) to help distinguish between new lesions and old lesions. It's injected intravenously to further enhance the sensitivity of the T1-weighted MRI scan. Gadolinium-based contrast agents are dangerous in patients with kidney disease. The contrast agent is normally chelated as it is expected to pass through the body quickly. In patients with kidney disease, the excretion is slower and the gadolinium becomes unbound, causing serious health issues.

Gadolinium-enhancing lesion
A lesion appearing on magnetic resonance imagery (MRI), following injection of the chemical compound gadolinium, that reveals a breakdown in the blood-brain barrier. This breakdown of the blood-brain barrier indicates either a newly active lesion or the re-activation of an old one, indicating disease activity.
(See: Gadolinium)

Gait or difficulty in walking, are among the most common mobility limitations in MS. The problems include muscle weakness, muscle tightness or spasticity, loss of balance, sensory deficit, and fatigue.

Gastro colic reflex
A mass peristaltic (coordinated, rhythmic, smooth muscle contraction that acts to force food through the digestive tract) movement of the colon that often occurs fifteen to thirty minutes after ingesting a meal.

(See: Percutaneous endoscopic gastrostomy)

Ganglia (singular: Ganglion)
Colonies of autonomic or sensory neurons (cell bodies) outside the brain and spinal cord acting to control local functions or transmit information to the CNS.

The study of inheritance patterns of specific traits.
(See: Genetic Definitions)

A band-like pain around the torso.

Glatiramer acetate
Glatiramer acetate is a treatment for relapsing-remitting multiple sclerosis (MS) that may extend the amount of time between relapses.

Glucocorticoid hormones
Steroid hormones that are produced by the adrenal glands in response to stimulation by adrenocorticotropic hormone (ACTH) from the pituitary. These hormones, which can also be manufactured synthetically (prednisone, prednisolone, methylprednisolone, betamethasone, dexamethasone), serve both an immunosuppressive and an anti-inflammatory role in the treatment of MS exacerbations: they damage or destroy certain types of T-lymphocytes that are involved in the overactive immune response, and interfere with the release of certain inflammation-producing enzymes.

A modification of protein that occurs in mammalian cell production that involves the addition of chains of sugar molecules to the amino acid chain, producing a carbohydrate structure similar to that found in natural proteins, such as interferon beta.

Gray or Grey matter
The neuronal layer or unmyelinated neuron layer of the brain used for routing sensory or motor stimulus and then responds to the stimuli.

Guillain-Barré syndrome (GBS)
An inflammatory disorder of the peripheral nerves characterized by rapid onset of weakness and often paralysis of the legs, arms, breathing muscles, and face.

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Heel-knee-shin test
A test of coordination in which the person is asked, with eyes closed, to place one heel on the opposite knee and slide it up and down the shin.

Helper T lymphocytes or T cells
White blood cells that are a major contributor to the immune system's inflammatory response against myelin.

Weakness or partial paralysis affecting one side of the body.

Paralysis of one side of the body including one arm and one leg.

Herniated disc
Condition in which the gelatinous core material of a disc bulges or ruptures out of its normal position and may exert pressure on the surrounding nerve root and/or spinal cord.

The part of the brain that plays a significant role in the formation of long-term memories.

The property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition.

Anatomic Orientation - Parallel to the floor, a plane passing through the standing body parallel to the floor.

Human genome
The total set of genes (approximately 90,000 to 100,000) arranged on two sets of 23 chromosomes in most cells of the human body.
(See: Genetic Definitions: Human genome)

Human Immunodeficiency Virus (HIV)
Human Immunodeficiency Virus (HIV) gradually destroys the body's immune system, thereby leaving the body open to attack by other viruses, bacteria, or other harmful foreign substances. After HIV has destroyed a certain amount of the body's immune system, the infection progresses to Acquired Immune Deficiency Syndrome (AIDS). To date, there is no way for HIV to be completely eradicated once it enters the body.

Human leukocyte antigens (HLA)
A group of molecules that are located on the surface of cells and that are unique in each organism, enabling the body to distinguish self from nonself. Also called the major histocompatibility complex.

A region of the brain in partnership with the pituitary gland that controls the hormonal processes of the body as well as temperature, mood, hunger, and thirst.

A supposition or assumption advanced as a basis for reasoning or argument, or as a guide to experimental investigation.

Pathological oxygen deprivation to body tissues.

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Meaning any disease arising spontaneously that is from an obscure, uncertain or unknown origin.

Infectious disease
An infectious disease is a disease caused by bacterial, viral, fungal, or protozoan infection. Though some infectious diseases are not contagious, others may be transmitted from animal to person (bird flu and cat scratch disease) or from person to person (MRSA, HIV, and other STDs).

Inversion recovery (IR)
Inversion recovery is an MRI technique, which can be wherein the nuclear magnetization is inverted at a time on the order of T1 before the regular imaging pulse-gradient sequences. The resulting partial relaxation of the spins in the different structures being imaged can be used to produce an image that depends strongly on T1. This may bring out differences in the appearance of structures with different T1 relaxation times. T1 in a given region can be calculated from the change in the MRI signal from the region due to the inversion pulse compared to the signal with no inversion pulse or an inversion pulse with a different inversion time. This sequence involves successive 180° and 90° pulses. The inversion recovery sequence is specified in terms of three parameters, inversion time (TI), repetition time (TR) and echo time (TE).

IgG antibodies are found in all body fluids and are among the five major types of antibodies. They are the smallest but most common antibody (75 to 80%) of all the antibodies in the body. IgG antibodies are very important in fighting bacterial and viral infections.

Immune-mediated disease
A disease in which components of the immune system (such as t-cells, antibodies, and others) are responsible for the disease either directly (as occurs in autoimmunity) or indirectly (as occurs when damage to the body occurs secondary to an immune assault on a foreign antigen such as a bacteria or virus).

Immune cells
cells produced in our bodies that protect us from disease-causing agents by producing antibodies.

Immune complex
Antibody attached to an antigen.

Immune response
The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful to the body. The immune system protects the body from potentially harmful substances by recognizing and responding to antigens.

Immune system
The immune system protects the body against potentially harmful substances, also called antigens. When the immune system detects an antigen, it initiates the immune response. This is a complex series of events that work together to eliminate the threat the antigen poses to the body.

Immune system disorders
Immune system or autoimmune disorders occur when the immune response is inappropriate, excessive, or lacking.

Idiopathic thrombocytopenic purpura (ITP)
Idiopathic thrombocytopenic purpura is a bleeding disorder in which the immune system destroys platelets, which are necessary for normal blood clotting. Persons with the disease have too few platelets in the blood. ITP is sometimes called immune thrombocytopenic purpura.

An insusceptibility that usually results from previous exposure to an infectious agent, either naturally or by vaccination.

Vaccination or immunization is a way to trigger the immune response. Small doses of an antigen, such as dead or weakened live viruses, are given to activate immune system "memory" (activated B cells and sensitized T cells).

Immunocompetent cells
White blood cells that defend against invading agents in the body.

Immunodeficiency disorder
Immunodeficiency disorders are an example of when the immune response is lacking.

Immunoglobulins (Ig)
Also known as immunoglobulins, they are proteins that are secreted by white blood cells called B-lymphocytes in response to the presence of a foreign substance. There are five antibody isotypes known as IgA, IgD, IgE, IgG and IgM.

Immunoglobulin G (IgG)
An antibody produced by human plasma cells. It's also found in plaques of a diseased central nervous system. Levels of IgG are increased in the cerebrospinal fluid of most MS patients.

The ability of a property enabling a substance to provoke an immune response, or the degree to which a substance possesses this property.

The science that concerns the body’s mechanisms for protecting itself from abnormal or foreign substances.

Immunomodulating drug
Changing the function of the immune systems by either increasing or decreasing its response to a given antigen or agent.

Immunomodulators are a type of multiple sclerosis (MS) treatment that can be used in patients with relapsing forms. Immunomodulators work to alter a patient’s immune system so that the MS disease course may change. This may result in fewer and less severe multiple sclerosis symptoms, and also slow the disease’s progression. When immunomodulators work, they can reduce a patient’s chances of disability, and thereby have the potential to enhance future quality of life.

Refers to the gradual deterioration of the immune system brought on by natural age advancement. It involves both the host’s capacity to respond to infections and the development of long-term immune memory.

An agent that can suppress or prevent the immune response.

In MS, a form of treatment that slows or inhibits the body's natural immune responses, including those directed against the body’s own tissues. Examples of immunosuppressive treatments in MS include mitoxantrone, cyclosporine, methotrexate, and azathioprine.

A medical treatment to stimulate a patient's immune system to attack and destroy disease-causing cells or using the immune system to treat disease.

The loss of function psychologically, physiologically, or anatomically.

In vivo
Latin for "within the living" refers to experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research.

Also called spontaneous voiding; the inability to control passage of urine or bowel movements.

The incidence of a disease is the number of new cases occurring in a given period of time in a given population.

Induction therapy
A short-duration, intense immunosuppression followed by initiation of interferon beta or similar treatment.

Anatomic Orientation - Below, as opposed to superior.

Anatomic Orientation - Below and to one side. Both inferior and lateral.

A tissue’s immunologic response to injury, characterized by mobilization of white blood cells and antibodies, swelling, and fluid accumulation. Also the body's characteristic reaction to infection or injury, resulting in redness, swelling, heat, and pain.

An infusion is the process of flowing a solution into the body, usually through a vein.

Innate immunity
Innate, or nonspecific, immunity is a defense system that you are born with and will protects you against all antigens.

The supply or conduction of nervous impulses to a muscle or body part.

A type of messenger or cytokine secreted by some white blood cells to affect other white blood cells.

These are multipolar neurons that connect afferent and efferent neurons within the CNS.

Intention tremor
Rhythmic shaking that occurs during a purposeful movement.

Interferon (IFN)
A group of immune system proteins, produced and released by cells infected by a virus, which inhibit viral multiplication and modify the body's immune response. Three interferon beta medications have been approved by the U.S. Food and Drug Administration (FDA) for treating relapsing forms of MS: IFN beta-1b (Betaseron); IFN beta-1b (Extavia); IFN beta-1a (Avonex); and IFN beta-1a (Rebif).

Interferon gamma
A naturally-occurring substance in the body, produced primarily by activated T cells, which promotes inflammation and is thought to be involved in MS exacerbations. Once tried as a treatment for MS, it was found to make the disease worse. Interferon beta works to counteract the effects of interferon gamma.

Internuclear ophthalmoplegia
A disturbance of coordinated eye movements in which the eye turned outward to look toward the side develops nystagmus (rapid, involuntary movements) while the other eye simultaneously fails to turn completely inward. This neurologic sign, of which the person is usually unaware, can be detected during the neurologic exam.

Intervention name
The generic name of the precise intervention being studied.

Primary interventions being studied: types of interventions are Drug, Gene Transfer, Vaccine, Behavior, Device, or Procedure.

Intradermal (ID)
Introduced into the skin.

Intramuscular (IM)
Injected into the muscle.

Intranuclear inclusions
Circumscribed masses of foreign or metabolically inactive materials, within the Cell Nucleus. Some are Viral Inclusion Bodies.

Intrathecal space
The space surrounding the brain and spinal cord that contains cerebrospinal fluid.

Intravenous (IV)
Within a vein typically to administer a medication.

Investigational new drug
A new drug, antibiotic drug, or biological drug that is used in a clinical investigation. It also includes a biological product used in vitro for diagnostic purposes.

Anatomic Orientation - The motion of a body part as it tilts toward the midline.

Involuntary emotional expression disorder (IEED)
Also known as pseudobulbar affect, this is characterized by outbursts of crying or laughter, but without corresponding emotions behind these outbursts.
(See: Pseudobulbar affect)

Having the same intensity as another object. Used to describe the results of imaging tests, such as x-rays, MRIs, or CT scans. Isoinetnse to muscle means having the same intensity as muscle on a scan.

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The Junction or articulation of two or more bones that permits varying degrees of motion between the bones.

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K Cells
Lymphocyte-like effector cells which mediate antibody-dependent cell cytotoxicity. They kill antibody-coated target cells which they bind with their Fc receptors.

Killer or Cytotoxic T cell
A T cell that attaches to foreign or abnormal cells and kills them.

Kurtzke Functional System Scores
Eight subscales that aim to measure the neurological function in eight different systems and are accumulated to provide the EDSS. The functional systems are pyramidal, cere-bellar, brainstem, sensory, bowel and bladder, visual, cerebral or mental, and other or miscellaneous functions. All but the last are graded from 0 (normal) to maximal impairment (grade 5 or 6).

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L-Hermitte's sign
Abnormal sensation of electricity or "pins and needles" going down the spine to the arms and legs when the neck is bent forward and the chin touches the chest.

The flattened or arched part of the vertebral arch, forming the roof or back part of the spinal canal.

Anatomic Orientation - Situated on the side, or away from the midline of the body.

Damaged area in the brain or spinal cord caused by demyelination (also called plaque or sclerosis).

Lesion load
Total volume of brain tissue affected by the MS disease process (as seen on MRI T2-weighted scans).

Leukemia is cancer of the blood that occurs when bone marrow begins to produce abnormal white blood cells, or leukemia cells. These abnormal cells eventually begin to outnumber other cells in the blood, making it difficult for the blood to do its job in the body properly. There are many different types of leukemia, each named for the type of leukemia cell most present in the body.

A white blood cell. A cellular component of the blood that lacks hemoglobin, has a nucleus, is capable of motility, and defends the body against infection and disease by ingesting foreign materials and cellular debris, by destroying infectious agents, or by producing antibodies.

Having abnormally high numbers of white blood cells, usually the result of a non-viral infection.

Having abnormally low numbers of white blood cells.

Fibrous connective tissue that links together bones at joints or that passes between bones of the spine.

Limbic system
A group of interconnected structures of the brain that mediate emotions, learning and memory as well as primitive responses such as eating and drinking.

Lorentz force
In physics, this is the force on a point charge due to electromagnetic fields.

Lumbar puncture (lp)
A lumbar puncture, also called a spinal tap, is a diagnostic procedure that uses a hollow needle (canula) to penetrate the spinal canal at the level of third–fourth or fourth–fifth lumbar vertebrae to remove cerebrospinal fluid for analysis. This procedure is used to examine the cerebrospinal fluid for changes in composition that are characteristic of MS (e.g., elevated white cell count, elevated protein content, the presence of oligoclonal bands).

Lumbar spine
The lower back region of the spine, which consists of the five vertebrae between the ribs and the pelvis.

Lyme Disease
A disease that affects the joints, nervous system, and heart that is transmitted by the deer tick and is caused by the bacteria Borrelia burgdorferi.

Lymphatic System
The lymphatic system is a network of vessels and tissues composed of lymph, an extracellular fluid, and lymphoid organs, such as lymph nodes. The lymphatic system is a conduit for travel and communication between tissues and the bloodstream. Immune cells are carried through the lymphatic system and converge in lymph nodes, which are found throughout the body.

A type of white blood cell that is part of the immune system. Lymphocytes can be subdivided into two main groups: B-lymphocytes, which originate in the bone marrow and produce antibodies; T-lymphocytes, which are produced in the bone marrow and mature in the thymus. Helper T-lymphocytes heighten the production of antibodies by B-lymphocytes; suppressor T-lymphocytes suppress B-lymphocyte activity and seem to be in short supply during an MS exacerbation.

Lymphoma is a type of blood cancer that starts in the lymphatic system, a part of the body’s immune system. The lymphatic system includes lymph nodes, the spleen and bone marrow. When a person has lymphoma, the lymphocytes, or white blood cells, in the lymphatic system become lymphoma cells. The lymphoma cells then reproduce to create lymphoma cell masses, which can crowd out and hinder the other, healthy cells working in that part of the body.

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A white blood cell with scavenger characteristics that has the ability to ingest and destroy foreign substances such as bacteria and cell debris.

Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI) is a method of creating images of the inside of the body. MRI uses powerful magnets and radio waves to produce these images. Along with other devices, MRI may help confirm or determine a diagnosis. MRI can be particularly helpful when diagnosing disorders of the brain or spine because they can provide detailed pictures of certain regions of the body that are difficult to see using other types of scanning devices. MRI allows the neurologist to identify MS lesions in the brain and spinal cord, at different stages of their development. T1 scans and T2 scans refer to the different scanning sequences to help distinguish tissue features.

Major histocompatibility complex
The major histocompatibility complex (MHC) is a large genomic region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproductive success.

A general feeling of bodily discomfort and being unwell.

Malignant MS
Rare and rapidly forming course of MS.

Mast cell
A connective tissue cell whose normal function is unknown but which is frequently injured in allergic reactions, releasing chemicals including histamine that are very irritating and cause itching, swelling, and fluid leakage from cells. These allergic chemicals may also cause muscle spasm and lead to lung and throat tightening, as in asthma. Also known as a mastocyte or labrocyte.

Mechanism of action
A mechanism of action describes the physical and chemical processes that bring about a particular action or reaction. For example, the mechanism of action of a drug details how exactly the drug reacts with body cells, tissue, or organs to produce the intended outcome.

Medulla oblongata
The part of the brain that contains centers for the control of vital processes such as heart rate, respiration, blood pressure, and swallowing.

Anatomic Orientation - In the middle or inside, as opposed to lateral.

A thin covering surrounding a cell and separating it from the environment; consists of a double layer of molecules called phospholipids and has proteins embedded in it.

The membrane covering the brain and spinal cord. A tumor arising from this tissue is called a meningioma.

MHC class II modulator
A treatment for RRMS that is presumed to change the way the immune system responds by working on inflammatory cells outside and inside the CNS.

Microgram (mcg)
A metric unit of mass equal to 0.001 milligram (mg) or one millionth of a gram.

Milligram (mg)
A metric unit of mass equal to 0.001 gram or 1000 micrograms.

Minimal record of disability (MRD)
A standardized method for quantifying the clinical status of a person with MS and is made up of five parts: Demographic Information; the Neurological Functional Systems, which assign scores to clinical findings for each of the various neurologic systems in the brain and spinal cord (pyramidal, cerebellar, brainstem, sensory, visual, mental, bowel and bladder); the Expanded Disability Status Scale, which gives a single composite score for the person's disease; the Incapacity Status Scale, which is an inventory of functional disabilities relating to activities of daily living; the Environmental Status Scale, which provides an assessment of social handicap resulting from chronic illness.

Physiology it is any of the various types of sensation, such as vision or hearing.

Molecular mimicry
This is an attack on self that occurs due to cross reactivity between a self-antigen and a pathogen protein.

A molecule is defined as a sufficiently stable, electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds.

Monoclonal antibodies (MAB, MoAb)
Antibodies that can be programmed to react on specific antigens suppressing the immune response and are produced by a clone or genetically homogeneous population of fused hybrid cells. Hybrid cells are cloned to establish cell lines producing a specific antibody that is chemically and immunologically homogeneous.

Monofocal episode
The person experiences a single neurologic sign or symptom (such as loss of vision) that's caused by a single lesion.

Mononucleosis or Mono
An infectious, viral disease which occurs mostly in adolescents and young adults due to the Epstein-Barr virus. EBV infection is believed a risk factor for MS development with a higher risk in patients infected as teenagers than as children. The transmission of Mono not only occurs from exchanging saliva, but also from contact with the airborne virus.

Weakness or paresis affecting a single extremity or part of one.

A single drug or therapy not to be used in combination with any other disease-modifying drug or therapy.

Morbidity refers to a diseased state, disability, or poor health due to any cause. This can be used to refer to the existence of any form of disease, or to the degree that the health condition affects a patient.

Motor neurons
(See: Efferent neurons)

Multifocal episode
The person experiences more than one sign or symptom (such as a loss of vision accompanied by weakness on one side) caused by lesions in more than one place.

Mucosal Tissue
Mucosal surfaces are prime entry points for pathogens, and specialized immune hubs are strategically located in mucosal tissues like the respiratory tract and gut. For instance, Peyer's patches are important areas in the small intestine where immune cells can access samples from the gastrointestinal tract.

Multiple sclerosis (MS)
Also known as disseminated sclerosis or encephalomyelitis disseminata, MS is an autoimmune condition in which the immune system attacks the central nervous system, leading to demyelination. MS was first described in 1868 by Jean-Martin Charcot. MS affects the ability of nerve cells in the brain and spinal cord to communicate with each other. Nerve cells communicate by sending electrical signals called action potentials down long fibers or axons, which are wrapped in an insulating substance called myelin. In MS, the body's own immune system attacks and damages the myelin. When myelin is lost, the axons can no longer effectively conduct signals. The name multiple sclerosis refers to the many scars in the white matter of the brain and spinal cord, which is mainly composed of myelin.

Multiple sclerosis fatigue
MS fatigue is a type of fatigue that can affect 75 to 95% of MS patients. It can affect a person’s ability to complete simple, daily tasks. It may occur because the energy required for him or her to move or breathe is far greater than the energy a non-MS patient would need to do the same thing leaving a patient completely exhausted.

Multiple sclerosis functional composite (MSFC)
A three-part, standardized, quantitative assessment instrument for use in clinical trials in MS, that was developed by the Task Force on Clinical Outcomes Assessment appointed by the National MS Society’s Advisory Committee on Clinical Trials of New Agents in MS. The three components of the MSFC measure leg function/ambulation (Timed 25-Foot Walk), arm/hand function (9-Hole Peg Test), and cognitive function (Paced Auditory Serial Addition Test (PASAT)).

Multiple Sclerosis (PPMS): Primary-Progressive
Primary-progressive multiple sclerosis accounts for about 10% of MS diagnoses. This type of MS is characterized by a slow and steady worsening of central nervous system (CNS) functioning, the symptoms of which include difficulty with balance, movement, and walking, and loss of vision. There are no flare-ups or exacerbations in primary-progressive MS, but the rate of disease progression occasionally may speed up, slow down, or even temporarily reverse.

Multiple Sclerosis (PRMS): Progressive-Relapsing
(note: outdated and no longer used as of 2013)
Progressive-relapsing multiple sclerosis affects about 5% of MS patients. It is characterized by constant disease progression and steady worsening of disease symptoms, as well as by acute, intermittent flare-ups, or exacerbations.

Multiple Sclerosis (RRMS): Relapsing-Remitting
Relapsing-remitting multiple sclerosis accounts for about 85% of all initial MS diagnoses. This type of MS is characterized by isolated relapses, also known as flare-ups, attacks, or exacerbations. During each relapse, there is a noticeable worsening of nervous system functioning. The symptoms of this may include difficulty with balance and movement, dizziness, and fatigue. When the patient is not having a relapse, he or she is partially or completely without symptoms.

Multiple Sclerosis (SPMS): Secondary-Progressive
Secondary-progressive multiple sclerosis develops in approximately 50% of relapsing-remitting MS patients within 10 years of the initial diagnosis. In secondary-progressive MS, the occasional relapses the patient initially experienced gradually change into constant, steadily worsening symptoms. These are indicative of the increasing dysfunction of the central nervous system (CNS). The relapses, or flare-ups, may or may not continue, and the patient may experience intermittent, temporary remission of symptoms.

Muscle tone
A characteristic of a muscle brought about by the constant flow of nerve stimuli to that muscle, which describes its resistance to stretching. Abnormal muscle tone can be defined as: hypertonus (increased muscle tone, as in spasticity); hypotonus (reduced muscle tone); flaccid (paralysis); atony (loss of muscle tone). Muscle tone is evaluated as part of the standard neurologic exam in MS.

A tenderness or pain in the muscles themselves.

Myasthenia gravis
A disorder affecting the space between the nerve and the muscle (neuromuscular junction) that results in transient motor weakness of the face and limbs.

A soft, white coating of nerve fibers in the central nervous system (CNS), composed of lipids (fats) and protein. Myelin serves as insulation and as an aid to efficient nerve fiber conduction. When myelin is damaged in MS, nerve fiber conduction is faulty or absent. Impaired bodily functions or altered sensations associated with those demyelinated nerve fibers are identified as symptoms of MS in various parts of the body.

Myelin basic protein
One of several proteins associated with the myelin of the central nervous system (CNS), which may be found in higher than normal concentrations in the cerebrospinal fluid of individuals with MS and other diseases that damage myelin.

An inflammatory disease of the spinal cord. In transverse myelitis, the inflammation spreads across the tissue of the spinal cord, resulting in a loss of its normal function to transmit nerve impulses up and down, as though the spinal cord had been severed.

An X-ray procedure by which the spinal canal and the spinal cord can be visualized. It's performed in conjunction with a lumbar puncture and injection of a special X-ray contrast material into the spinal canal.

The pathology of the spinal cord.

A quick, involuntary muscle jerk.

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Natural history study
Study of the natural development of something (such as an organism or a disease) over a period of time.

Natural killer cells
These cells that mediate a form of innate immunity known as natural killing by targeting and causing lysis of virus-infected or tumor cells.

Death or decay of tissue that results from loss of the blood supply and oxygen needed to keep tissue alive and healthy.

(See: No Evidence of Disease Activity)

Nephrogenic systemic fibrosis (NSF)
Formerly known as nephrogenic fibrosing dermopathy (NFD), is a rare and serious syndrome that involves fibrosis of skin, joints, eyes, and internal organs. Its cause is not fully understood, but it seems to be associated with exposure to gadolinium (which is used as a contrast substance for MRI) in patients with multiple sclerosis (MS).

This is a poisonous effect of some substances (both toxic chemicals and medication) on the kidneys.

A bundle of nerve fibers or tissue that conducts electrical impulses (messages) from the brain and spinal cord to all other parts of the body and/or conveys sensory information from the body to the central nervous system (CNS). The fibers are either afferent (leading toward the brain and serving in the perception of sensory stimuli of the skin, joints, muscles, and inner organs) or efferent (leading away from the brain and mediating contractions of muscles or organs).

Nerve block
A procedure used to relieve otherwise intractable spasticity, including painful flexor spasms. An injection of phenol into the affected nerve interferes with the function of that nerve for up to three months, potentially increasing a person's comfort and mobility.

Nerve palsy
Diplopia can be cause by the following cranial nerve palsies: Third nerve palsy (oculomotor) – inability to move the eye normally in all directions. Fourth nerve palsy (trochlear) – causes vertical double vision (diplopia) because of the inability of the eyes to maintain proper alignment. Sixth nerve palsy (abducens) – causes horizontal double vision (diplopia) with in turning of the eye and decreased lateral movement.

Nerve root
The initial portion of a spinal nerve as it originates from the spinal cord.

Nervous system
Includes all of the neural structures in the body: the central nervous system consists of the brain, spinal cord, and optic nerves; the peripheral nervous system consists of the nerve roots, nerve plexi, and nerves throughout the body.

Pain that begins along a nerve and not from the source that it appears from.

Excessive exhaustion or tiredness that would look as if it were from physical causes.

Nerve inflammation and direct damage that is part of a degenerative process.

Permanent damage or loss of nerve cells, which include neurons and axons.

Neurodegenerative disease
A condition in which cells of the brain and spinal cord are lost.

Refers to the relationship between the body’s nervous system and endocrine system, whereby certain cells in the body release hormones in response to a neural stimulus.

The birth of new cells and the process by which new nerve cells are generated.

Related to activity of the nervous system, such as in neurogenic bladder.

Neurogenic bladder
Bladder dysfunction associated with neurologic malfunction in the spinal cord and characterized by a failure to empty, failure to store, or a combination of the two. Symptoms that result from these three types of dysfunction include urinary urgency, frequency, hesitancy, nocturia, and incontinence.

Neurological fatigue
A feeling of overwhelming lassitude or tiredness that can occur any time of the day and for any length of time.

Neurogenic pain
This type of chronic pain is caused by damage to the central or peripheral nervous system. The types of neurogenic pain are central pain syndrome, trigeminal neuralgia, and phantom pain.

A medical doctor or physician with specialized training in the diagnosis and treatment of conditions that affect the nervous system. Many have a specialized interest in MS, epilepsy, or Parkinson’s disease.

Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue, such as muscle.

The basic nerve cell of the nervous system. A neuron consists of a nucleus within a cell body and one or more processes (extensions) called dendrites and axons.

Neuropathic pain
A state of chronic pain associated with damage to nerve fibers causing a shooting or burning pain along with tingling or numbness.

Disease of the peripheral nerves.

A condition resulting from damage to the peripheral nerves that results in weakness or sensory loss and pain in the arms, hand, legs, and feet.

A general term used to describe the adaptive changes in the structure or function of nerve cells or groups of nerve cells in response to injuries to the nervous system or alterations in patterns of their use and disuse.

A psychologist with specialized training in the evaluation of cognitive functions. Neuropsychologists use a battery of standardized tests to assess specific cognitive functions and identify areas of cognitive impairment. They also provide remediation for individuals with MS-related cognitive impairment.

Neural arch
The bony arch of the back part of a vertebra that surrounds the spinal cord, also referred to as the vertebral arch.

Neutralizing antibodies (NAbs)
Proteins produced by the body that may block or neutralize the effectiveness of a drug therapy.

A white blood cell that ingests and kills bacteria and other foreign cells.

No Evidence of Disease Activity (NEDA)
(pronounced NEE-dah) It means no relapses, no disability progression, and no new or enlarging lesions on MRI.

It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue. This activity is initiated by nociceptors or pain receptors that can detect mechanical, thermal or chemical changes, above a set threshold. Once stimulated, a nociceptor transmits a signal along the spinal cord, to the brain. Nociception triggers a variety of autonomic responses and may also result in the experience of pain in sentient beings.

Nocturia is the frequent need to awaken and urinate at night. People with nocturia may get up six or more times per night to urinate. Treatment for nocturia may involve medication and testing to determine underlying causes.

Rapid, involuntary movements of the eyes in the horizontal or, occasionally, the vertical direction.

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OB/GYN (obstetrician/ gynecologist)
An obstetrician/gynecologist (OB/GYN) is a physician who both delivers babies and treats diseases of the female reproductive organs.

Occipital lobe
Helps process visual information.

Occupational therapist (OT)
Occupational therapists assess functioning in activities of everyday living, including dressing, bathing, grooming, meal preparation, writing, and driving, which are essential for independent living. In making treatment recommendations, the OT addresses (1) fatigue management, (2) upper body strength, movement, and coordination, (3) adaptations to the home and work environment, including both structural changes and specialized equipment for particular activities, and (4) compensatory strategies for impairments in thinking, sensation, or vision.

Off-label use
A drug prescribed for conditions other than those approved by the FDA.

Oligoclonal bands
A diagnostic sign indicating abnormal levels of certain antibodies in the cerebrospinal fluid. It shows a series of distinct bands found in the immunoglobulin (a protein substance from immune cells) of the cerebrospinal fluid (CSF). The bands may be present in other conditions, but are helpful in diagnosing MS if other MS symptoms are present.

A type of cell in the CNS that makes and supports myelin.

Olmstead decision
The Supreme Court decision in Olmstead v L.C. (1999) is an interpretation of Title II of the Americans with Disabilities Act (ADA) that affirms the right of people with disabilities to receive services in the most integrated setting appropriate to their needs. The decision recognizes that unnecessary segregation of persons in long-term care facilities constitutes discrimination under the ADA. (1999) is an interpretation of Title II of the Americans with Disabilities Act (ADA) that affirms the right of people with disabilities to receive services in the most integrated setting appropriate to their needs. The decision recognizes that unnecessary segregation of persons in long-term care facilities constitutes discrimination under the ADA.

Optic atrophy
A wasting of the optic disc that results from partial or complete degeneration of optic nerve fibers and is associated with a loss of visual acuity.

Optic chiasm
Located beneath the hypothalamus and is where the optic nerve crosses over to the opposite side of the brain.

Optic disc
The small blind spot on the surface of the retina where cells of the retina converge to form the optic nerve; the only part of the retina that is insensitive to light.

Optic neuritis
Inflammation or demyelination of the optic nerve transient or permanent impairment of vision along with pain. The optic nerve comprises axons that emerge from the retina of the eye and carry visual information to the primary visual nuclei, most of which is relayed to the occipital cortex of the brain to be processed into vision. Inflammation of the optic nerve causes loss of vision usually because of the swelling and destruction of the myelin sheath covering the optic nerve. Direct axonal damage may also play a role in nerve destruction in many cases.

Orphan drugs
An FDA category that refers to medications used to treat diseases and conditions that occur rarely. There is little financial incentive for the pharmaceutical industry to develop medications for these diseases or conditions. Orphan drug status, however, gives a manufacturer specific financial incentives to develop and provide such medications.

Continuous, involuntary, and chaotic eye movements that result in a visual disturbance in which objects appear to be jumping or bouncing.

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An unpleasant sensation that can range from mild, localized discomfort to agony. Pain has both physical and emotional components. The physical part of pain results from nerve stimulation. Pain may be contained to a discrete area, as in an injury, or it can be more diffuse, as in disorders like fibromyalgia . Pain is mediated by specific nerve fibers that carry the pain impulses to the brain where their conscious appreciation may be modified by many factors.

Pain - Neuropathic
(See: Neuropathic pain)

Pain management
The process of providing medical care that alleviates or reduces pain. Pain management is an extremely important part of health care, as patients forced to remain in severe pain often become agitated and/or depressed and have poorer treatment outcomes. Mild to moderate pain can usually be treated with analgesic medications, such as aspirin or ibuprofen. For chronic or severe pain, opiates and other narcotics are often used, sometimes in concert with analgesics; with steroids or non-steroidal anti-inflammatory drugs when the pain is related to inflammation; or with anti-depressants, which can potentiate some pain medications without raising the actual dose of the drug, and which affect the brain's perception of pain. Narcotics carry with them a potential for side effects and addiction, so patients and caregivers must weigh the level of pain against these dangers in the pain management process. The risk of addiction is not normally a concern in the care of terminal patients.

Something that helps manage symptoms of, but does not cure, a disease.

Parahippocampal gyrus
An important connecting pathway of the brains limbic system.

The inability to move part of the body.

A weakness but not total paralysis of the lower extremities or legs.

Paralysis of both lower extremities or legs.

Parasympathetic nervous system
Division of the autonomic nervous system that controls normal digestive, reproductive, cardiopulmonary, and vascular functions and stimulates most secretions. This subsystem works as a direct antagonist to the sympathetic division, and functions are balanced by their interaction.

The functional parts of an organ in the body, such as the central nervous system (CNS). This is in contrast to the stroma, which refers to the structural tissue of organs, namely, the connective tissues.

Partial or incomplete paralysis of a part of the body.
(See: Monoparesis, Paraparesis, Hemiparesis & Quadraparesis)

A partial sensation of burning, prickling, tingling, or creeping on the skin.

Parietal lobe
The part of the brain that receives and processes information about temperature, taste, touch, and movement coming from the rest of the body. Reading and arithmetic are also processed in this region.

Parkinson's disease (PD)
Parkinson's disease belongs to a group of conditions called motor system disorders, which are the result of the loss of dopamine-producing brain cells. The four primary symptoms of PD are tremor, or trembling in hands, arms, legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination. PD is both chronic, meaning it persists over a long period of time, and progressive, meaning its symptoms grow worse over time.

Paroxysmal spasm
A sudden, uncontrolled limb contraction that occurs intermittently, lasts for a few moments, and then subsides.

Paroxysmal symptom
Any one of several symptoms that have sudden onset, apparently in response to some kind of movement or sensory stimulation, last for a few moments, and then subside. Paroxysmal symptoms tend to occur frequently in those individuals who have them, and follow a similar pattern from one episode to the next. Examples of paroxysmal symptoms include: acute episodes of trigeminal neuralgia (sharp facial pain), tonic seizures (intense spasm of limb or limbs on one side of the body), dysarthria (slurred speech often accompanied by loss of balance and coordination), and various paresthesias (sensory disturbances ranging from tingling to severe pain).

Passive immunity
Passive immunity involves antibodies that are produced in a body other than your own.

The mode of development of a disease.

This is the ability of a pathogen to produce an infectious disease in an organism and often used interchangeably with the term "virulence", although some authors prefer to reserve the latter term for descriptions of the relative degree of damage done by a pathogen. Virulence is the ability of an organism to invade the bloodstream.

The bony part of each side of the neural arch of a vertebra that connects the lamina (back part) with the vertebral body (front part).

Peginterferon is a covalent conjugate of recombinant interferon and polyethylene glycol (PEG), with the former moiety responsible for the biological activity.

Percutaneous endoscopic gastrostomy (PEG)
A PEG is a tube inserted into the stomach through the abdominal wall to provide food or other nutrients when eating by mouth is not possible. The tube is inserted in a bedside procedure using an endoscope to guide the tube through a small abdominal incision. An endoscope is a lighted instrument that allows the doctor to see inside the stomach.

Percutaneous rhizotomy
An outpatient surgical procedure used in the management of severe, intractable trigeminal neuralgia. The surgeon makes a tiny incision in the side of the person’s face and blocks the function of the trigeminal nerve using laser surgery, cryosurgery (freezing), or cauterization.

Peripheral nerves
Nerves outside the brain and spinal cord.

Peripheral nervous system (PNS)
Controls muscles, glands, and provides sensory information to and from the CNS.

Periventricular region
The area surrounding the four fluid-filled cavities within the brain. MS plaques are commonly found within this region.

Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria and dead or dying cells. They are essential for fighting infections and subsequent immunity.

The process of a cell engulfing and ingesting an invading microorganism, another cell, or a cell fragment.

Phantom pain
Also called "ghost" pain, it's a type of neurogenic pain that occurs in paralyzed patients or as a result of limb amputation.

The processes in a living organism of absorption, distribution, metabolism, and excretion of a drug or vaccine.

This refers to the general study of all of the many different genes that determine drug behavior.

This refers to the study of inherited differences or variation in drug metabolism and response.

The study of how the body absorbs, distributes, breaks down, and eliminates drugs.

The scientific field that studies how the body reacts to medicines and how medicines affect the body.
A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions between the two.

A phosphene is an entoptic phenomenon characterized by the experience of seeing light without light actually entering the eye. Spots of light that are produced when pressure is placed on the eye. Closed-eye visualizations (CEV) are a form of phosphene.

Physical medicine and rehabilitation (PM&R) or physiatry (pronounced /fɨˈzaɪ.ətri/). Physicians who specialize in physical medicine and rehabilitation, including the diagnosis and management of musculoskeletal injuries and pain syndromes, electrodiagnostic medicine (such as electromyography), and rehabilitation of severe impairments, including those caused by neurologic disease or injury.
(See: Electromyography (EMG))

Physical therapist (PT)
Physical therapists are trained to evaluate and improve movement and function of the body, with particular attention to physical mobility, balance, posture, fatigue, and pain. The physical therapy program typically involves (1) educating the person with MS about the physical problems caused by the disease, (2) designing an individualized exercise program to address the problems, and (3) enhancing mobility and energy conservation through the use of a variety of mobility aids and adaptive equipment.

The study of how living organisms function.

Pineal gland
Controls the response to light and dark. The exact role of the pineal gland is not certain.

Pituitary gland
A small, bean-sized organ that is located at the base of the brain and is connected to the hypothalamus by a stalk. The pituitary gland secretes many essential hormones for growth and sexual maturation.

Plantar reflex
A reflex response obtained by drawing a pointed object along the outer border of the sole of the foot from the heel to the little toe. The normal flexor response is a bunching and downward movement of the toes. An upward movement of the big toe is called an extensor response, or Babinski reflex, which is a sensitive indicator of disease in the brain or spinal cord.

Anatomic Orientation - A downward motion of a body part.

An area of inflamed or demyelinated central nervous system (CNS) tissue.

Plasma cell
A lymphocyte-like cell found in the bone marrow, connective tissue, and blood that is involved in the body’s immune system.
(See: Lymphocyte)

Plasma exchange
Plasma exchange involves removing blood from the person, mechanically separating the blood cells from the fluid plasma, mixing the blood cells with replacement plasma, and returning the blood mixture to the body. The rationale for plasma exchange is that the plasma contains immune factors that may stimulate disease activity. Substituting replacement plasma may dilute the strength of these potentially destructive immune factors. However, the detailed mechanisms involved are not yet clearly understood.

A total or near total of muscle strength.
(See: Parapleia, Hemiplegia, Quadraplegia)

The part of the brain that contains centers for the control of vital processes, including respiration and cardiovascular functions. It also is involved in the coordination of eye movements and balance.

Position sense
The ability to tell, with one’s eyes closed, where fingers and toes are in space. Position sense is evaluated during the standard neurologic exam in MS.

Anatomic Orientation - The back or rear side of the body.

Anatomic Orientation - From back to front, as opposed to anteroposterior.

This is the period just after delivery and refers to the mother and postnatal to the baby.

Postural tremor
Tremor present when the limbs or trunk are kept in certain positions and when they are moved actively, usually due to near-synchronous rhythmic bursts in opposing muscle groups. Rhythmic shaking that occurs when the muscles are tensed to hold something or stay in a specific position.

Power grading
A measurement of muscle strength used to evaluate weakness or paralysis. Power is tested as part of the standard neurologic exam in MS.

The number of all new and old cases of a disease in a defined population at a particular point in time. The prevalence of MS in the United States at any given time is about 1/750 — approximately 400,000 people.

Primary-Progressive MS (PPMS)
(See: Multiple Sclerosis (PPMS): Primary-Progressive)

Prediction of the future course of the disease.

Progressive-Relapsing MS (PRMS)
(See: Multiple Sclerosis (PRMS): Progressive-Relapsing)

Progressive multifocal leukoencephalopathy (PML)
Progressive multifocal leukoencephalopathy (PML) is caused by the reactivation of a common virus in the central nervous system of immune-compromised individuals. Polyomavirus JC (often called JC virus) is carried by a majority of people and is harmless except among those with lowered immune defenses. The disease occurs, rarely, in organ transplant patients; people undergoing chronic corticosteroid or immunosuppressive therapy; and individuals with cancer, such as Hodgkin’s disease, lymphoma, and sarcoidosis. PML is most common among individuals with acquired immune deficiency syndrome (AIDS). It's an opportunistic viral infection of the brain that usually causes severe disability or death.

Anatomic Orientation - Rotation of the forearm and hand so that the palm is down (and the corresponding movement of the foot and leg with the sole down), as opposed to supination.

Anatomic Orientation - With the front or ventral surface downward (lying face down), as opposed to supine.

It is the sense of the relative position of neighboring parts of the body. Unlike the six exteroceptive senses (sight, taste, smell, touch, hearing, and balance) by which we perceive the outside world, and interoceptive senses, by which we perceive the pain and the stretching of internal organs, proprioception is a third distinct sensory modality that provides feedback solely on the status of the body internally. It is the sense that indicates whether the body is moving with required effort, as well as where the various parts of the body are located in relation to each other.

Prospective memory
The ability to remember an event or commitment scheduled for the future. Thus, a person who agrees to meet or call someone at a given time on the following day must be able to remember the appointment when the time comes. People with MS-related memory impairment frequently report problems with this type of memory for upcoming appointments.

Anatomic Orientation - Located closer or upstream. Toward the beginning, as opposed to distal.

Neuropathic itch can originate at any point along the afferent pathway as a result of damage of the nervous system.

A temporary aggravation of disease symptoms, resulting from an elevation in body temperature or other stressor (e.g., an infection, severe fatigue, constipation), that disappears once the stressor is removed. A pseudo-exacerbation involves symptom flare-up rather than new disease activity or progression.

Pseudobulbar affect (PBA)
A dramatic disorder of emotional expression and regulation characterized by uncontrollable episodes of laughing and crying that often cause embarrassment, curtailment of social activities, and reduction in quality of life. The disorder occurs in patients with brain injury caused by many types of neurological disease.

A condition of personality following frontal lobe lesion in which apathy, indifference and a loss of initiative are apparent symptoms but are not accompanied by a sense of depression in the patient.

A personality disorder in which there are oddities of thought (magical thinking, paranoid ideation, suspiciousness), perception (illusions, depersonalization), speech (digressive, vague, over elaborate), and behavior (inappropriate affect in social interactions, frequently social isolation) that are not severe enough to characterize schizophrenia.

Pyramidal tracts
Motor nerve pathways in the brain and spinal cord that connect nerve cells in the brain to the motor cells located in the cranial, thoracic, and lumbar parts of the spinal cord. Damage to these tracts causes spastic paralysis or weakness.

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Partial or incomplete paralysis affecting all four limbs.

Paralysis distinguished by the loss of motion, reflexes, and sensation in the trunk of the body in addition to both legs and arms.

Quantitative Neurological Examination
A battery of tests used to measure cognition, strength, steadiness, reaction, speed, coordination, sensation, fatigue, gait, station and selected skills of daily living. It has been used in some multiple sclerosis trials, but is not widely accepted.

Quality of life or Supportive care trials
Refers to trials that explore ways to improve comfort and quality of life for individuals with a chronic illness.

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Recent memory
The ability to remember events, conversations, content of reading material or television programs from a short time ago, i.e., an hour or two ago or last night. People with MS-related memory impairment typically experience greatest difficulty remembering these types of things in the recent past.

A molecule on a cell's surface or inside the cell that allows only molecules that fit precisely in or attach to it, just like a key fits in its lock.

Produced by a biotechnological process in the laboratory.

An involuntary response of the nervous system to a stimulus, such as the stretch reflex, which is elicited by tapping a tendon with a reflex hammer, resulting in a contraction. Increased, diminished, or absent reflexes can be indicative of neurologic damage, including MS, and are therefore tested as part of the standard neurologic exam.

Regulatory or Suppressor T cell
A white blood cell that helps end or suppress an immune response.

Rehabilitation in MS involves the intermittent or ongoing use of multidisciplinary strategies (e.g., physiatry, physical therapy, occupational therapy, speech therapy) to promote functional independence, prevent unnecessary complications, and enhance overall quality of life. It's an active process directed toward helping the person recover and/or maintain the highest possible level of functioning and realize his or her optimal physical, mental, and social potential given any limitations that exist. Rehabilitation is also an interactive, ongoing process of education and enablement in which people with MS and their care partners are active participants rather than passive recipients.

Relapsing-Remitting MS (RRMS)
(See: Multiple Sclerosis (RRMS): Relapsing-Remitting)

A lessening in the severity of symptoms or their temporary disappearance during the course of the illness.

Remote memory
The ability to remember people or events from the distant past. People with MS tend to experience few, if any, problems with their remote memory.

The repair of damaged myelin, usually very slow and uncontrollable in MS.

Restless legs syndrome
A common neurological disorder that causes pulling, tearing, and jerking sensations in the legs when a person is at rest.

Retrobulbar neuritis
Retrobulbar neuritis is a form of optic neuritis in which the optic nerve, which is at the back of the eye, becomes inflamed. The inflamed area is between the back of the eye and the brain. The optic nerve contains fibers that carry visual information from the nerve cells in the retina to the nerve cells in the brain. When these fibers become inflamed, visual signaling to the brain becomes disrupted, and vision is impaired.
(See: Optic Neuritis)

Reynolds number
In fluid mechanics, the Reynolds number (Re) is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions.

Pronounced: rī-zot′ŏ-mē - Rhizotomy is a neurosurgical procedure that selectively severs or cuts problematic nerve roots in the spinal cord, most often to relieve the symptoms of neuromuscular conditions.

Right-hand rule
In this case it is used in situations where a vector must be assigned to the rotation of a body, a magnetic field or a fluid.

Risk-benefit ratio
The risk to individual participants versus the potential benefits. The risk/benefit ratio may differ depending on the condition being treated.

Romberg's sign
The inability to maintain balance in a standing position with feet and legs drawn together and eyes closed.

Twisting movement of one vertebra on another as a patient turns from one side to the other.

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Part of the pelvis just above the coccyx (tailbone) and below the lumbar spine (low back).

Anatomic Orientation - A vertical plane passing through the standing body from front to back. The mid-sagittal, or median plane, splits the body into left and right halves.

Scanning speech
Abnormal speech characterized by staccato-like articulation that sounds clipped because the person unintentionally pauses between syllables and skips some of the sounds.

A lay term indicating pain along the course of the sciatic nerve, especially noted in the back of the buttocks and running down the back of the leg and thigh and below the knee.

A hardening of tissue. In MS, sclerosis is the body's replacement of lost myelin around CNS nerve cells with scar tissue.

Abnormal lateral or sideways curvature of the spine.

A gap or blind spot in the visual field.

Secondary-Progressive MS (SPMS)
(See: Multiple Sclerosis (SPMS): Secondary-Progressive)

An abnormal electrical discharge of brain cells (neurons) that results in a transient disturbance in brain function.

This is the faculty by which stimuli are perceived and conditions outside and within the body are distinguished and evaluated. The major senses are sight, hearing, smell, taste, touch, and pressure. Other senses include hunger; thirst; pain; temperature; proprioception; and spatial, temporal, and visceral sensations.

Sense organs
The organs of special sense including eye, olfactory organ, gustatory organs. All organs containing sensory receptors.

Related to bodily sensations such as pain, smell, taste, temperature, vision, hearing, acceleration, and position in space.

A cell or bacterium that has combined with specific antibody to form a complex capable of reacting with component.

Sensory neurons
(See: Afferent neurons)

A clinical condition in which infectious agents (bacteria, fungi) or products of infection (bacterial toxins) enter the blood and profoundly affect body systems.

Serine endopeptidases or serine proteases
These are proteases (enzymes that cut peptide bonds in proteins) in which one of the amino acids at the active site is serine.

Shingles (herpes zoster) is a viral infection that affects adults. It is caused by the varicella-zoster virus, the same virus that causes chickenpox in children. When a person has shingles, he or she will break out in a painful rash on a portion of the body. Shingles is often triggered by stress in adults that had chickenpox as children, but it can also appear in people with weakened immune systems. This may include patients taking therapies that suppress the immune system, HIV/AIDS patients, and patients with certain types of cancer.

Side effects
Any undesired actions or effects of a drug or treatment. Negative or adverse effects may include headache, nausea, hair loss, skin irritation, or other physical problems. Experimental drugs must be evaluated for both immediate and long-term side effects.
(See: Adverse reaction)

An objective physical problem or abnormality identified by the physician during the neurologic examination. Neurologic signs may differ significantly from the symptoms reported by the patient because they are identifiable only with specific tests and may cause no overt symptoms. Common neurologic signs in multiple sclerosis include altered eye movements and other changes in the appearance or function of the visual system; altered reflexes; weakness; spasticity; circumscribed sensory changes.

Signal transduction
The process by which a hormone or growth factor outside the cell transmits a message into the cell.

For the immune system, the skin is usually the first line of defense against microbes. Skin cells produce and secrete important antimicrobial proteins, and immune cells can be found in specific layers of skin.

Somantic nervous system (SNS)
A part of the PNS that has conscious and voluntary control of body movements and gives relation to the environment.

Somatosensory evoked potential
A test that measures the brain’s electrical activity in response to repeated (mild) electrical stimulation of different parts of the body. Demyelination results in a slowing of response time. SNPs, which make up about 90% of all human genetic variation, occur every 100 to 300 bases along the 3-billion-base human genome.

Symptom of spasticity in which the legs and/or arms straighten (extended) or flexed (bend) suddenly into a stiff positions. These spasms, which typically last for several seconds to minutes, occur most commonly in bed at night, but may occur with attempted movement and are fairly common in MS. These two types of spasms are know respectively as extensor and flexor spasms.

Abnormal increase of muscle tone or stiffness giving resistance to being moved.

Speech/language pathologist
Speech/language pathologists specialize in the diagnosis and treatment of speech and swallowing disorders. A person with MS may be referred to a speech/language pathologist for help with either one or both of these problems. Because of their expertise with speech and language difficulties, these specialists also provide cognitive remediation for individuals with cognitive impairment.

Spinal canal
A bony channel located in the vertebral column that protects the spinal cord and nerve roots.

Spinal cord
The longitudinal cord of nerve tissue that is enclosed in the spinal canal. It serves not only as a pathway for nerve impulses to and from the brain, but also as a center for carrying out and coordinating reflex actions independently of the brain.

Spinal stenosis
Abnormal narrowing of the vertebral column that may result in pressure on the spinal cord, spinal sac, or nerve roots arising from the spinal cord.

Spinal tap
(See: Lumbar puncture)

The flexible bone column extending from the base of the skull to the tailbone. It's made of 33 bones known as vertebrae. The spine is also referred to as the vertebral column, spinal column or backbone.

The spleen is an organ located behind the stomach. While it's not directly connected to the lymphatic system, it's important for processing information from the bloodstream. Immune cells are enriched in specific areas of the spleen, and upon recognizing blood-borne pathogens, they will activate and respond accordingly.

Inflammation of vertebrae.

The forward displacement or "slippage" of one vertebra on another.

Degenerative bony changes in the spine, usually most marked at the vertebral joints.

Spontaneous mutations
Changes to the genetic information due to errors in replication, repair, or recombination of DNA sequences.

Stance ataxia
An inability to stand upright due to disturbed coordination of the involved muscles, which results in swaying and a tendency to fall in one or another direction.

Standard treatment
A treatment currently in wide use and approved by the FDA, considered to be effective in the treatment of a specific disease or condition.

Standards of care
Treatment regimen or medical management based on state of the art participant care.

A stricture in a vein caused by an abnormal narrowing of the vein itself, or by the protrusion or impinging of some other anatomical component against the vein.

(See: ACTH, Corticosteroid & Glucocorticoid hormones)

Structural biology
A field of study dedicated to determining the three-dimensional structures of biological molecules to better understand the function of these molecules.

Subcutaneous (SubQ)
Injected into the fat layer under the skin and above the muscles. After the injection, the drug moves into small blood vessels and the bloodstream. The subcutaneous route is used with many protein and polypeptide drugs such as interferons which, if given by mouth, would be broken down and digested in the intestinal tract.

Subcutaneous fat
The third layer of skin, located below the dermis and composed mainly of fat cells and blood vessels.

Anatomic Orientation - On the surface or shallow, as opposed to deep.

Anatomic Orientation - Situated above or directed upward, toward the head of an individual.

Anatomic Orientation - Rotation of the forearm and hand so that the palm is upward (and the corresponding movement of the foot and leg), as opposed to pronation.

Anatomic Orientation - With the back or dorsal surface downward (lying face up), as opposed to prone.

Suppressor T-lymphocytes
White blood cells that act as part of the immune system and may be in short supply during an MS exacerbation.

Part of the nervous system that is in charge of involuntary body functions such as our heart, organs and glands. The sympathetic nervous system originates in the spinal cord.

A subjectively perceived problem or complaint reported by the patient. In multiple sclerosis, common symptoms include visual problems, fatigue, sensory changes, weakness or paralysis of limbs, tremor, lack of coordination, poor balance, bladder or bowel changes, and psychological changes.

Having the characteristics of a particular disease but arising from another cause.

Symptomatic drugs
Medicines that help alleviate some symptoms.

Symptomatic treatment
Therapy that eases the symptoms without addressing the basic cause of the disease.

A group of symptoms that collectively indicate or characterize a disease, psychological disorder, or other abnormal condition.

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T1 weighted images
Also referred to as T1WI or "spin-lattice" relaxation time, is one of the basic pulse sequences in MRI and demonstrates differences in the T1 relaxation times of tissues.

T2 weighted images
The "pathology weighted" MRI sequence. Because most pathology contains more water than normal tissue around it, it's usually brighter on T2.

T cell (T lymphocyte)
A lymphocyte (white blood cell) that develops in the bone marrow, matures in the thymus, and works as part of the immune system in the body. A white blood cell that is involved in specific immunity and that may be one of three types: helper, killer (cytotoxic), or regulatory.

T cell activation
This occurs in a non-specific manner secondary to release of CNS antigens into the periphery following a toxic CNS insult.

T regulatory cell
These express high levels of CD25 and are capable of suppressing the function of other T cells and inhibiting in vivo immune responses. They contribute to natural protection against autoimmunity.

Tait–Bryan angles
Also called Yaw, pitch, and roll, is named after Peter Guthrie Tait and George H. Bryan, are a specific kind of Euler angles used to define the relative orientation of an object with respect to some reference orientation, usually a set of reference axes. The three angles specified in this formulation are defined as the roll angle, pitch angle, and yaw angle. Used in this case as anatomical terms of location for magnetic resonance imaging (MRI).

Tandem gait
A test of balance and coordination that involves alternately placing the heel of one foot directly against the toes of the other foot.

Temporal lobe
Processes hearing, memory and language functions.

An irreversible surgical procedure performed to cut severely contracted tendons attached to muscles that do not respond to any other type of spasticity control and are causing intractable pain and skin complications related to lack of physical movement.

Is a unit of magnetic field, magnetic flux density, or magnetic induction.

A major relay station of the brain between the senses and the cortex (the outer layer of the brain consisting of the parietal, occipital, frontal and temporal lobes). Located near the center of the brain and controls input and output to and from the brain, as well as the sensation of pain and attention.

Therapeutic drug
A drug used to treat a disease or condition; contrast with drug of abuse.

Thoracic spine
The region of the spine attached to the ribcage, between the cervical and lumbar areas, which consists of 12 vertebrae.

For the immune system, T cells mature in the thymus, a small organ located in the upper chest.

Antibody titer is a laboratory test that measures the level of antibodies in a blood sample. The antibody level in the blood tells your doctor whether or not you have been exposed to an antigen or something that the body thinks is foreign. The body uses antibodies to attack and remove foreign substances.

Ringing in the ears.

Gradual stepping up of a dose of medicine. It allows the body to adjust and become used to the medicine's effects, thereby reducing the likelihood and severity of potential side effects that may occur at the beginning of a treatment.

A form of tremor, resulting from demyelination in the cerebellum, that manifests itself primarily in the head and neck.

Tonic seizure
An intense spasm that lasts for a few minutes and affects one or both limbs on one side of the body. Like other types of paroxysmal symptoms in MS, these spasms occur abruptly and fairly frequently in those individuals who have them, and are similar from one brief episode to the next. The attacks may be triggered by movement or occur spontaneously.

Total lesion load
The total number of lesions.

An adverse effect produced by a drug that is detrimental to the participant's health. The level of toxicity associated with a drug will vary depending on the condition which the drug is used to treat.

In neuroscience, tractography is a procedure to demonstrate the neural tracts. It uses special techniques of magnetic resonance imaging (MRI), and computer-based image analysis. The results are presented in two- and three-dimensional images.

Transcutaneous electric nerve stimulation (TENS)
TENS is a non-addictive and noninvasive method of pain control that applies electric impulses to nerve endings via electrodes that are attached to a stimulator by flexible wires and placed on the skin. The electric impulses block the transmission of pain signals to the brain.

Transient ischemic attack (TIA)
The neurological symptoms that result from transient interruption of blood flow to the brain.

Anatomic Orientation - A horizontal plane passing through the standing body parallel to the ground.

Transverse myelitis
An acute attack of inflammatory demyelination that involves both sides of the spinal cord. The spinal cord loses its ability to transmit nerve impulses up and down. Paralysis and numbness are experienced in the legs and trunk below the level of the inflammation.

Uncontrollable shaking of any or multiple parts of the body.

Trigeminal neuralgia
Also called tic douloureux, it's a disorder of the fifth cranial nerve that causes a lightning-like or electric shock-like acute pain in the face. It's caused by demyelination of nerve fibers at the site where the sensory (trigeminal) nerve root for that part of the face enters the brainstem.

Transverse myelitis
Demyelination involving both sides of the spinal core causing paralysis and numbness occurs in the legs and trunk below the level of inflammation.

A systematic exposition or argument in writing including a methodical discussion of the facts and principles involved and conclusions reached.

An adverse reaction from a drug that is detrimental to someone's health.

The study of how poisonous substances interact with living organisms.

(See: Genetic Definitions)

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Relating to, occurring on, appearing on, or involving one side of the body.

Duct or tube that drains the urinary bladder.

Urge or urgency
A strong desire to void.

Urinary frequency
Feeling the urge to urinate even when urination has occurred very recently.

Urinary hesitancy
The inability to void urine spontaneously even though the urge to do so is present.

Urinary urgency
The inability to postpone urination once the need to void has been felt.

A physician who specializes in the branch of medicine (urology) concerned with the anatomy, physiology, disorders, and care of the male and female urinary tract, as well as the male genital tract.

A medical specialty that deals with disturbances of the urinary (male and female) and reproductive (male) organs.

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Relating to blood vessels.

A compensatory technique that involves raising the heel on the stronger leg to make it easier to swing the weaker leg through.

Venous Obstruction
Any type of stenosis, blockage, malformation, or other abnormality in the vein that significantly impedes venous blood flow. To be considered significant, a venous obstruction must impede =50% of the blood flow through the vein.

Anatomic Orientation - Pertaining to the front or anterior of any structure. The ventral surfaces of the body include the chest, abdomen, shins, palms, and soles. Ventral is as opposed to dorsal. From the Latin "venter" meaning belly.

Ventricles of the brain are connected cavities within the brain, where cerebrospinal fluid is produced.

Vertebra or Vertebrae
The 33 bones that make up the spine, individually referred to as a vertebra. They are divided into the cervical spine (neck), the thoracic spine (upper back or rib cage), the lumbar spine (lower back), and the sacral spine (pelvis or base of the spine).

Anatomic Orientation - Upright, as opposed to horizontal.

A dizziness or imbalance of equilibrium that usually causes a spinning sensation or whirling motion, often accompanied by nausea and vomiting.

Vestibular system
The parts of the nervous system that control equilibrium and balance and that coordinate head and eye movement.

Vibration sense
The ability to feel vibrations against various parts of the body. Vibration sense is tested (with a tuning fork) as part of the sensory portion of the neurologic exam.

The ability of an organism to invade the bloodstream.

An infectious agent composed of a protein coat around a DNA or RNA core; to reproduce, viruses depend on living cells.

Visual acuity
Clarity of vision. Acuity is measured as a fraction of normal vision. 20/20 vision indicates an eye that sees at 20 feet what a normal eye should see at 20 feet; 20/400 vision indicates an eye that sees at 20 feet what a normal eye sees at 400 feet.

Visual evoked potential
A test in which the brain’s electrical activity in response to visual stimuli (e.g., a flashing checkerboard) is recorded by an electroencephalograph and analyzed by computer. Demyelination results in a slowing of response time. Because this test is able to confirm the presence of a suspected brain lesion (area of demyelination) as well as identify the presence of an unsuspected lesion that has produced no symptoms, it is extremely useful in diagnosing MS. VEPs are abnormal in approximately 90 percent of people with MS.

Vocational rehabilitation (VR)
Vocational rehabilitation is designed to enable people with disabilities to become or remain employed. Originally mandated by the Rehabilitation Act of 1973, VR programs are carried out by individually created state agencies. In order to be eligible for VR, a person must have a physical or mental disability that results in a substantial handicap to employment. VR programs typically involve evaluation of the disability and need for adaptive equipment or mobility aids, vocational guidance, training, job-placement, and follow-up.

A volumetric pixel (volumetric picture element) is a volume element, representing a value on a regular grid in three-dimensional space. This is analogous to a pixel, which represents 2D image data in a bitmap (also called a pixmap). Voxels are frequently used in the visualization and analysis of medical and scientific data such as MRI.

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White blood cells
White blood cells, or leukocytes, defend the body by attacking and destroying antigens, such as viruses, bacteria and other infections. They are produced in the bone marrow and are always present in the body. However, the number of white blood cells will usually increase significantly when they are fighting a disease or infection. The five types of white blood cells are lymphocytes, monocytes, neutrophils, basophils, and eosinophils.

White matter
A lipid-rich myelinated portion of the brain and spinal cord that is comprised mostly of myelinated nerve fibers giving it a white texture that function as conduit for passing information.

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X-rays are primarily used for diagnostic radiography and crystallography. As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. X-rays are a form of ionizing radiation and as such can be dangerous. X-rays span 3 decades in wavelength, frequency and energy. From about 0.12 to 12 keV they are classified as soft X-rays, and from about 12 to 120 keV as hard X-rays, due to their penetrating abilities. X-rays are shorter in wavelength than UV rays. (An electron volt (eV) is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt. This also states that 1000 times would, therefore be a kilo-electron volt (keV)).

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