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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.

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 (brain, spinal cord).

See Detrusor-external sphincter dyssynergia.

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

Detrusor-external sphincter dyssynergia (DESD)   
See Combined (bladder) dysfunction.

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.

Short for deoxyribonucleic acid, DNA constitutes the chemical basis for genes, the basic units of heredity. See Gene.

Double-blind clinical study   
A study in which none of the participants, including experimental subjects, examining doctors, attending nurses, or any other research staff, know 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.

Poorly articulated speech resulting from dysfunction of the muscles controlling speech, usually caused by damage to the central nervous system or a peripheral motor nerve. The content and meaning of the spoken words remain normal.

Distorted or unpleasant sensations experienced by a person when the skin is touched, that are typically caused by abnormalities in the sensory pathways in the brain and spinal cord.

A disturbance of coordination, caused by lesions in the cerebellum. A tendency to over- or underestimate the extent of motion needed to place an arm or leg in a certain position as, for example, in overreaching for an object.

Difficulty in swallowing. It is a neurologic or neuromuscular symptom that may result in aspiration (whereby food or saliva enters the airway), slow swallowing (possibly resulting in inadequate nutrition), or both.

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.

See Experimental allergic encephalomyelitis.

See Electroencephalography.

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)   
Electromyography is a diagnostic procedure that records muscle electrical potentials through a needle or small plate electrodes. The test can also measure the ability of peripheral nerves to conduct impulses.

See Electromyography.

Erectile dysfunction
The inability to attain or retain a rigid penile erection.

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.

Unrealistic cheerfulness and optimism, accompanied by a lessening of critical faculties; generally considered to be a result of damage to the brain.

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 Brainstem auditory evoked potential; Somatosensory evoked potential; Visual evoked potential.

The appearance of new symptoms or the aggravation of old ones, lasting at least twenty-four 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.

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.

Failure to empty (bladder)   
A type of neurogenic bladder dysfunction in MS resulting from demyelination in the voiding reflex center of the spinal cord. The bladder tends to overfill and become flaccid, resulting in symptoms of urinary urgency, hesitancy, dribbling, and incontinence.

Failure to store (bladder)   
A type of neurogenic bladder dysfunction in MS resulting from demyelination of the pathways between the spinal cord and brain. Typically seen in a small, spastic bladder, storage failure can cause symptoms of urinary urgency, frequency, incontinence, and nocturia.

See Food and Drug Administration.

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.

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.

Foley catheter   
See Indwelling catheter.

Food and Drug Administration (FDA)   
The U.S. federal agency that is responsible for enforcing governmental regulations pertaining to the manufacture and sale of food, drugs, and cosmetics. Its role is to prevent the sale of impure or dangerous substances. Any new drug that is proposed for the treatment of MS in the United States 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.

Frontal lobes   
The largest lobes of the brain. The anterior (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.

A chemical compound that can be administered to a person during magnetic resonance imaging to help distinguish between new lesions and old lesions.

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. See Gadolinium.

Gastrocolic 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.

A basic unit of heredity containing coded instructions for manufacturing a protein. Genes are subunits of chromosomes, which are strands of DNA contained within most cells.

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.

Health care proxy   
See Advance (medical) directive.

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   
White blood cells that are a major contributor to the immune system’s inflammatory response against myelin.

Weakness of one side of the body, including one arm and one leg.

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

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. The Human Genome Project is an international program that was launched in 1990 to map the building blocks of DNA in the genome and determine the function of every gene. Although the mapping of DNA in the human genome has recently been completed, it will take many more years to identify the individual genes and determine their function. This endeavor is expected to provide further basic understanding of human genetics, as well as information that will contribute to the treatment and prevention of diseases.

Hyperbaric oxygen   
A procedure in which the person breathes oxygen under greater than atmospheric pressure in a specially constructed chamber. Once thought to be a potential treatment for MS, it has been evaluated in several controlled, double-blind studies and found to be ineffective for this purpose.

Reprinted with permission from Rosalind C. Kalb (ed.), Multiple Sclerosis: The Questions You Have—The Answers You Need, 3rd Edition. New York: Demos Medical Publishing, Inc., 2004

  Last updated October 2004