Glossary of Multiple Sclerosis Terms

There are a large number of terms specific to the diagnosis, treatment, and study of multiple sclerosis.

Please let your health care provider know if you have any questions about medical terms or would like more explanation about your treatment.

The National Multiple Sclerosis Society also publishes a full glossary of MS-related terms on its website.

Brief glossary

A - C D - F G - I J - L M - O P - R S - U V - Z

A protein produced by certain cells of the immune system, produced in response to bacteria, viruses, and other types of foreign antigens. See Antigen.

Any substance that triggers the immune system to produce an antibody. It generally refers to infectious or poisonous (toxic) substances in the body. See Antibody.

The lack of coordination and unsteadiness that result from the brain's failure to regulate the body's posture and the strength and direction of limb movements. Ataxia is most often caused by disease activity in the brain (cerebellum).

Autoimmune disease
A process in which the body's immune system causes illness by mistakenly attacking healthy cells, organs, or tissues in the body that are essential for good health. Multiple sclerosis is believed to be an autoimmune disease, along with many other conditions such as systemic lupus erythematosus, rheumatoid arthritis, and scleroderma. The precise origin of these diseases are not known.

The extension or prolongation of a nerve cell (neuron) that conducts impulses to other nerve cells or muscles. 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.

A type of lymphocyte (white blood cell) manufactured in the bone marrow that makes antibodies.

B cell depletion
An approach to MS therapy whereby B cells are depleted by targeting an protein on the surface of B cells, CD20, with therapeutic anti-CD20 antibodies. Current therapies using this approach are rituximab, ocrelizumab, and ofatumumab.

In clinical trials, sometimes at least one party involved in the clinical trial is unaware of which patients are receiving the experimental treatment and which are receiving the control substance. This is done in an attempt to eliminate bias in the interpretation of clinical trial outcomes. It indicates that trials may be either single-blind (patients do not know which treatment they are receiving) or double-blind (neither the examining physicians nor the patients know which treatment each patient is receiving).

Blood-brain barrier
A semipermeable cell layer around blood vessels in the brain and spinal cord that prevents large molecules, immune cells, and potentially damaging substances and disease-causing organisms (e.g., viruses) from passing out of the blood stream into the central nervous system (brain and spinal cord). A break in the blood-brain barrier may underlie the disease process in MS.

Cerebrospinal fluid (CSF)
A watery, colorless, clear fluid that bathes and protects the brain and spinal cord. The composition of this fluid can be altered by a variety of diseases. Certain changes in CSF that are characteristic of MS can be detected with a lumbar puncture (spinal tap), a test sometimes used to help make the MS diagnosis. See Lumbar puncture.

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.

Clinical trial
Strictly controlled studies designed to provide information that will allow for statistically valid evaluation of the safety and efficacy of a particular treatment. See also Double-blind clinical study and Placebo.

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

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. See also Immunosuppression.

A loss of myelin in the white matter of the central nervous system (brain, spinal cord).

Double-blind clinical study
A study in which none of the participants, including experimental subjects, examining doctors, attending nurses, or any other research staff, knows who is taking the test drug and who is taking a control or placebo agent. The purpose of this research design is to avoid inadvertent bias of the test results. In all studies, procedures are designed to "break the blind" if medical circumstances require it.

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. See also Visual evoked potential.

The appearance of new symptoms or the aggravation of old ones, lasting at least 24 hours (synonymous with attack, relapse, flare-up, or worsening); 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.

Gadolinium-enhancing lesion
A lesion appearing on magnetic resonance imagery, 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.

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 tissue's immunologic response to injury, characterized by mobilization of white blood cells and antibodies, swelling, and fluid accumulation.

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-1a (Avonex®); and IFN beta-1a (Rebif®).

L-Hermitte's sign
An abnormal sensation of electricity or "pins and needles" going down the spine into the arms and legs that occurs when the neck is bent forward so that the chin touches the chest.

Lumbar puncture
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).

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.

Magnetic resonance imaging (MRI)
A diagnostic procedure that produces visual images of different body parts without the use of X-rays. Nuclei of atoms are influenced by a high frequency electromagnetic impulse inside a strong magnetic field. The nuclei then give off resonating signals that can produce pictures of parts of the body. An important diagnostic tool in MS, MRI makes it possible to visualize and count lesions in the white matter of the brain and spinal cord.

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 Multiple Sclerosis. 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)).

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

Oligoclonal bands
A diagnostic sign indicating abnormal levels of certain antibodies in the cerebrospinal fluid; seen in approximately 90 percent of people with multiple sclerosis, but not specific to MS.

Optic neuritis
Inflammation or demyelination of the optic (visual) nerve with transient or permanent impairment of vision and occasionally pain.

An inactive, non-drug compound that is designed to look just like the test drug. It is administered to control group subjects in double-blind clinical trials (in which neither the researchers nor the subjects know who is getting the drug and who is getting the placebo) as a means of assessing the benefits and liabilities of the test drug taken by experimental group subjects.

An area of inflamed or demyelinated central nervous system tissue.

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.

Primary progressive MS
A clinical course of MS characterized from the beginning by progressive disease, with no plateaus or remissions, or an occasional plateau and very short-lived, minor improvements.

Progressive-relapsing MS
A clinical course of MS that shows disease progression from the beginning, but with clear, acute relapses, with or without full recovery from those relapses along the way.

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.

Randomized study
A clinical trial in which all patients are assigned randomly (by chance) to be in experimental group (receiving the experimental treatment) or the control group (receiving the placebo or control substance).

Relapsing-remitting MS
A clinical course of MS that is characterized by clearly defined, acute attacks with full or partial recovery and no disease progression between attacks.

The repair of damaged myelin. Myelin repair occurs spontaneously in MS but very slowly. Research is currently underway to find a way to speed the healing process.

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

Secondary-progressive MS
A clinical course of MS that initially is relapsing-remitting and then becomes progressive at a variable rate, possibly with an occasional relapse and minor remission.

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.

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.

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.

Theiler's murine encephalomyelitis-induced demyelinating disease (TMEV-IDD)
A model of MS in which Theiler's virus injection into mice results in an inflammatory, demyelinating progressively disabling resembling progressive forms of MS.

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.

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.

White matter
The part of the brain that contains myelinated nerve fibers and appears white, in contrast to the cortex of the brain, which contains nerve cell bodies and appears gray.