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

Acute disseminated encephalomyelitis (ADEM) — A one-time neurologic event that most often follows a viral illness, vaccination or immunization. ADEM doesn't require treatment and goes away on its own. In diagnosing childhood multiple sclerosis (MS), the doctor must determine whether a single episode of neurologic symptoms is ADEM or the beginning of MS.

Acute — Coming on suddenly; not chronic or long lasting.

Adrenocorticotropic hormone (ACTH) — Hormone produced by the pituitary gland, which stimulates the adrenal glands to produce cortisone.

Affective release — A condition in which episodes of laughing or crying occur for no apparent reason. Lesions in the limbic system, a group of brain structures involved in emotional feeling and expression, are believed to be the cause. Affective release is very rare in multiple sclerosis. Also called pseudo-bulbar affect.

Afferent pupillary defect — An abnormal reflex response to light that is a sign of nerve fiber damage due to optic neuritis. Normally, a pupil gets smaller when a light is shined either into that eye (direct response) or the other eye (indirect response). In an afferent pupillary defect, there is a relative decrease in the direct response.

Ankle-foot orthosis (AFO) — A brace, usually plastic, worn on the lower leg and foot to support the ankle and correct foot drop. By holding the foot and ankle in the correct position, the AFO promotes correct heel-toe walking. See Foot drop.

Antibodies — Immune system proteins that bind to bacteria, viruses and other types of antigens. In autoimmune diseases such as MS, antibodies may attack the body's own cells and tissues. See Antigen.

Anticholinergic — The action of certain medications often used to treat neurogenic bladder dysfunction. These medications inhibit the transmission of parasympathetic nerve impulses and thereby reduce spasms of smooth muscle in the bladder.

Antigen — A substance that triggers the immune system to produce an antibody or immune response; generally refers to infectious or toxic substances. See Antibody.

Assistive device — A tool that's made or adapted to assist a person in performing a particular task, such as a cane, walker or shower chair.

Ataxia — The unsteadiness and lack of coordination that results 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 cerebellum. Ataxia can affect any limb, the trunk or a person's gait.

Atrophy — A wasting or decrease in size of a body part because of disease or lack of use.

Attack — Sudden onset of new symptoms or worsening of old ones due to multiple sclerosis. Generally, these symptoms must last for more than 24 hours before it is considered an attack. Also called an exacerbation or relapse.

Auditory processing — The ability to recognize and remember information that you hear. For students, this is important in understanding classroom instructions and following directions.

Autoimmune disease — A condition in which the body's immune system causes illness by mistakenly attacking its own healthy cells, organs or tissues. Multiple sclerosis is believed to be an autoimmune disease, along with systemic lupus erythematosus, rheumatoid arthritis, scleroderma and many others.

Autonomic nervous system — The part of the nervous system that regulates body functions that aren't voluntary, such as the activity of the glands, heart muscle and smooth muscles such as the gut. The autonomic nervous system consists of the sympathetic nervous system — which accelerates heart rate, constricts blood vessels, and raises blood pressure — and the parasympathetic nervous system, which slows heart rate, increases intestinal and gland activity and relaxes sphincter muscles. The autonomic nervous system is rarely impaired in MS.

B-cell — A type of lymphocyte (a type of white blood cell) made in the bone marrow that produces antibodies.

Babinski reflex — A reflex produced by stroking the outside sole of the foot with a pointed object, causing the big toe to move up rather than the normal bunching and downward movement of the toes. This is frequent in MS.

Bell's palsy — A paralysis of a facial nerve, usually on one side of the face, which can be caused by MS or an infection. It appears suddenly and can be temporary or permanent.

Blood-brain barrier — A layer of cells surrounding blood vessels in the brain and spinal cord that prevents large molecules, immune cells and potentially damaging substances and organisms such as viruses from passing out of the blood stream and into the brain and spinal cord. A disruption of the blood-brain barrier may underlie the disease process in MS.

Brainstem — The part of the central nervous system that houses the nerve centers of the head as well as the centers for breathing and heart control. It extends from the base of the brain to the spinal cord and includes the pons and medulla.

Brainstem auditory evoked potential (BAEP) — A test in which the brain's electrical activity in response to sounds is recorded by an electroencephalograph and analyzed by computer. Demyelination slows the brain's response. BAEP is sometimes useful in the diagnosis of multiple sclerosis. Also called brainstem auditory evoked response, or BAER.

CAT Scan — See computerized axial tomography or CT scan.

Central nervous system — The part of the nervous system that includes the brain, optic nerves and spinal cord.

Cerebellum — A part of the brain, located behind the brainstem and under the cerebral hemispheres, that controls balance and coordination of movement.

Cerebrospinal fluid (CSF) — A watery, clear fluid that bathes and protects the brain and spinal cord. A variety of diseases can change the composition of this fluid, including multiple sclerosis (MS). Changes that are characteristic of MS can be detected with a lumbar puncture, a test sometimes used to help make the MS diagnosis. See Lumbar puncture.

Cerebrum — The large, upper part of the brain, which acts as a master control system and is responsible for initiating thought and movement. The cerebrum includes two hemispheres, left and right.

Chronic — Long lasting, not acute.

Clinical finding — An observation made during a medical exam that indicates a physical or mental change or impairment.

Clinical trial — A rigorously conducted study designed to test the safety and efficacy of a treatment. See also Double-blind clinical study, Placebo.

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

Cognition — 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 impairment — Changes in cognitive function caused by injury or disease. Some degree of cognitive impairment — particularly in memory, information processing and executive functions — occurs in about 50 to 60 percent of people with MS. See Cognition.

Cognitive rehabilitation — Techniques designed to improve cognitive functioning in people whose cognition is impaired because of injury or disease. Rehabilitation improves the impaired function via repetitive drills or practice, or compensates for impaired functions that aren't likely to improve. Cognitive rehabilitation is provided by psychologists and neuropsychologists, speech/language pathologists and occupational therapists.

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

Computerized axial tomography (CAT scan) — A non-invasive technique for examining soft tissues of the body. Also called CT scan.

Constipation — A condition in which bowel movements happen less frequently than is normal for the person, or the stool is small, hard and difficult or painful to pass.

Contraction — A shortening of muscle fibers that causes a joint to move.

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

Coordination — Muscles and muscle groups working together in an organized way to produce a movement such as grabbing an object, walking or standing.

Corpus callosum — The broad band of nerve fiber tissue that connects the two cerebral hemispheres of the brain. Multiple sclerosis plaques are commonly found within this region.

Cortex — The outer layer of brain tissue, which is made of gray matter (neuron bodies).

Corticosteroid — Any of the natural or synthetic hormones associated with the adrenal cortex. Corticosteroids include glucocorticoids, such as methylprednisolone or prednisone, which have an anti-inflammatory and immunosuppressive effect and are used to treat multiple sclerosis exacerbations. See also Glucocorticoids; Immunosuppression; Exacerbation.

Cortisone — A glucocorticoid steroid hormone, produced by the adrenal glands or made synthetically. Cortisone has anti-inflammatory and immunosuppressive effects. Prednisone, prednisolone, and methylprednisolone also belong to this group of substances.

Cranial nerves — Nerves that carry sensory, motor or parasympathetic fibers to the face and neck. Included among this group of twelve nerves are the optic nerve (vision), trigeminal nerve (sensation along the face), facial nerve (facial strength), oculomotor nerve (eye movement), and vagus nerve (pharynx and vocal cords). Evaluation of cranial nerve function is part of the standard neurologic exam.

Crystallized knowledge — Learned and stored knowledge and experience. For instance, vocabulary, spelling and ability to read.

Cerebrospinal (CSF) protein — This protein is normally dissolved in the spinal fluid and can be measured. It may increase when there is inflammation.

Cytokines — Messenger chemicals released by T-cells, a type of white blood cell, that signal and mobilize other components of the immune system or other organs.

Decubitus — A body position that causes undue pressure on certain parts of the body, which can lead to the eventual breakdown of skin and underlying tissue. Decubitus sores also are called bed sores or pressure sores.

Deep tendon reflexes — The involuntary jerks of the knee or elbow that are normally produced when the tendons are tapped. Reflexes are tested as part of the standard neurologic exam.

Dementia — A deteriorated mental state due to a disease process. It can result from many disorders of the nervous system.

Demyelinating disease — A disease causing loss or damage of myelin. Multiple sclerosis is one example of a demyelinating disease in the central nervous system, but other conditions can also lead to dymyelination.

Demyelination — A loss of myelin in the brain or spinal cord. Myelin is the outer covering of nerve cells.

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

Dexamethasone (Decadron) — A high potency glucocorticoid, or steroid, used to decrease swelling and inflammation in the nervous system.

Diplopia — Double vision, or seeing two images of the same object, when the two eyes fail to work in a coordinated fashion.

Disability — A restriction or lack of ability to perform an activity in the manner or within the range considered normal for a human being.

Double-blind clinical study — A study in which none of the participants, including experimental subjects, doctors, nurses or any other research staff, know who is taking the test drug and who is taking the control or placebo. The purpose is to avoid unintentional bias of the results.

Dysarthria — 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.

Dysesthesia — 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.

Dysmetria — 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. Caused by lesions in the cerebellum. See Finger-to-nose test and Heel-knee-shin test.

Dysphagia — Difficulty in swallowing that is often due to weakness or spasm of the esophagus. Dysphagia can cause aspiration (meaning food or saliva enters the airway), slow swallowing or both.

Dysphonia — Disorders of voice quality, including poor pitch control, hoarseness, breathiness and hypernasality. Caused by spasticity, weakness or lack of coordination of muscles in the mouth and throat.

Edema — Swelling caused by excessive amounts of fluid in the body's tissues.

EEG — See Electroencephalography.

Electroencephalography (EEG) — A diagnostic test that records, via electrodes attached to the head, electrical activity generated by brain cells. An EEG is useful in evaluating a person's tendency toward seizures.

Electromyography (EMG) — 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. EMG results are usually normal in multiple sclerosis (MS) patients, as MS doesn't affect the peripheral nervous system.

EMG — See Electromyography.

Etiology — 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 the agent invades the person's body.

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

Evoked potentials (EPs) — Diagnostic tests that record the nervous system's electrical response to the stimulation of specific sensory pathways such as visual, auditory and general sensory pathways. Demyelination results in a slowing of response time. EPs can demonstrate lesions along specific nerve pathways whether or not the lesions are producing symptoms, making this test useful in confirming the diagnosis of multiple sclerosis.

Exacerbation — The appearance of new symptoms or the aggravation of old ones. Exacerbations last at least twenty-four hours and are usually associated with inflammation and demyelination in the brain or spinal cord. Also called attack, relapse, flare or worsening.

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 found in MS patients, in which the bladder tends to overfill and become stretched and loose, resulting in symptoms of urinary urgency, hesitancy, dribbling and incontinence.

Failure to store (bladder) — A type of neurogenic bladder dysfunction found in MS patients, which can cause urinary urgency, frequency, incontinence and frequent night-time urination.

Finger-to-nose test — A test of coordination and intention tremor, in which the person is asked to touch the tip of the nose with the tip of the index finger, with the eyes closed. This test is part of the standard neurologic exam.

Flaccid — A decrease in muscle tone resulting in loose, "floppy" limbs.

Flare — The appearance of new symptoms or the aggravation of old ones. Also called relapse, attack or 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 seated.

Fluid reasoning — Learning ability that can influence the speed and amount that someone can learn, as well as the ability to manipulate and use information in a reasoning process. This is important for reading, solving problems and generating solutions.

Food and Drug Administration (FDA) — The U.S. federal agency responsible for enforcing governmental regulations of the manufacture and sale of food, drugs and cosmetics. The FDA must approve any new drug to treat MS.

Foot drop — Weakness in the foot and ankle muscles, caused by poor nerve conduction, which interferes with a person's ability to flex the ankle and walk with a normal heel-to-toe pattern. In foot drop, the toes touch the ground before the heel, causing the person to trip or lose balance.

Frontal lobes — The largest lobes of the brain, located at the front 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 front area of the frontal lobe is concerned with learning, behavior, judgment and personality.

Gadolinium — A kind of dye given to a person with multiple sclerosis during magnetic resonance imaging (MRI) to help distinguish between new lesions, which take up the dye, and old lesions, which don't.

Gamma globulin — Specific proteins found in normal human serum and cerebrospinal fluid. Seventy to 80 percent of persons with multiple sclerosis have increased levels of these proteins in the cerebrospinal fluid.

Glucocorticoid hormones — Steroid hormones produced by the adrenal glands or manufactured synthetically. Glucocorticoids have immunosuppressive and anti-inflammatory effects and are used to treat multiple sclerosis exacerbations Examples include prednisone, prednisolone, methylprednisolone, betamethasone and dexamethasone.

Handicap — A disadvantage, resulting from an impairment or disability, which interferes with a person's efforts to fulfill a role that's normal for that person. Handicap represents the social and environmental consequences of a person's impairments and disabilities.

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

Helper T-lymphocytes — White blood cells that are major contributors to the immune system's inflammatory response and play a key role in the attack on myelin seen in multiple sclerosis.

Hemiparesis — Weakness of one side of the body, including one arm and one leg, and sometimes half of the face.

Hemiplegia — Paralysis of one side of the body, including one arm and one leg, and sometimes half of the face.

Immune defect — General term describing different malfunctions of the immune system, in which the immune system either doesn't respond to a foreign substance by destroying or neutralizing it, or destroys normal body structures, as with an autoimmune disease. Examples of autoimmune diseases include lupus erythematosus, rheumatoid arthritis and multiple sclerosis.

Immune system — A complex system of various organs and cells that protect the body against disease-causing organisms and other foreign invaders.

Immunocompetent cells — Includes white blood cells (B-and T-lymphocytes and others) that defend against disease-causing organisms and other foreign invaders in the body.

Immunoglobulin — See Antibody.

Immunosuppression — In multiple sclerosis, a form of treatment that slows or inhibits the body's natural immune responses, including those directed against the body's own tissues.

Impairment — Any loss of function directly resulting from injury or disease.

Incidence — The number of new cases of a disease in a specified population over a defined period of time.

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

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

Information processing speed — How fast a person recognizes and remembers information.

Intention tremor — Rhythmic shaking that occurs when making a purposeful movement, such as reaching to pick something up or bringing an outstretched finger in to touch one's nose; can be related to cerebellar lesions, which can occur in multiple sclerosis.

Interferon — A group of immune system proteins, produced and released by cells infected by a virus, which interferes with the virus' attempts to reproduce itself and modifies the body's immune response. Synthetic interferons such as Betaseron, Rebif and Avonexare are used as preventive treatments in multiple sclerosis.

Internuclear ophthalmoplegia — A disturbance of eye coordination, in which the eye turned outward to look toward the side shows rapid, involuntary movements, while the other eye fails to turn completely inward. This can be detected during the neurologic exam, and may be associated with double vision.

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

Intravenous — Within a vein; often used in the context of an injection of medication into a vein, or infusion.

Lesion — See Plaque.

Leukocyte — White blood cell.

L'hermitte's sign — A 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 the chin touches the chest. It's typically related to a cervical spinal cord lesion, common in multiple sclerosis.

Long-term associative storage and retrieval — The ability to store information for a long period of time and recall it when needed.

Lumbar puncture — A diagnostic procedure in which a hollow needle is inserted into the spinal canal in order to remove cerebrospinal fluid for analysis. Also called spinal tap or CSF collection.

Lymphocyte — A type of white blood cell that's part of the immune system. Lymphocytes can be divided into two main groups: B-lymphocytes and T-lymphocytes. Helper T-lymphocytes promote immune responses, while suppressor T-lymphocytes suppress part of the immune response.

Lymphocytopheresis — Removal of white blood cells from the blood.

Macrophage — A white blood cell that can ingest and destroy foreign substances such as bacteria and cell debris. Macrophages play a key role in the immune response.

Magnetic resonance imaging (MRI) — A diagnostic procedure that produces visual images of the body without using X-rays. An important diagnostic tool in multiple sclerosis, MRI makes it possible to visualize and count some of the lesions in the white matter of the brain and spinal cord, and follow the progression of these lesions over time.

Monoclonal antibodies — Laboratory-produced antibodies, which can be programmed to react against a specific antigen to suppress the immune response. Some new therapies for multiple sclerosis are made of monoclonal antibodies.

Motor neurons — Nerve cells of the brain and spinal cord that enable various parts of the body to move.

MRI — See Magnetic resonance imaging.

Multiple Sclerosis (MS) — A chronic inflammatory disease of the central nervous system. MS is characterized by worsening and improvement of symptoms, called exacerbations and remission. Common symptoms include loss of strength, difficulty with balance and bladder control, numbness, tingling and blurred or double vision.

Muscle tone — A characteristic of a muscle that 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); or atony (loss of muscle tone). Muscle tone is evaluated as part of the standard neurologic exam in multiple sclerosis.

Myelin — A soft, white coating, made of fats and proteins, which surrounds the nerve fibers in the nervous system. Myelin serves as insulation and aids nerve fiber conduction; when myelin is damaged in multiple sclerosis (MS), this conduction is faulty or absent, causing MS symptoms.

Myelin basic protein (MBP) — One of the most abundant proteins contained in the myelin sheath of the central nervous system. MBP may be released in higher than normal concentrations in the cerebrospinal fluid of individuals with multiple sclerosis; however, people without multiple sclerosis may also have high concentrations of MBP.

Myelitis — 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.

Myelogram — An X-ray procedure that produces images of the spinal canal and the spinal cord.

Nerve — A bundle of nerve fibers, or axons. 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).

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.

Neurogenic — Related to activity of the nervous system.

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 include urinary urgency, frequency, hesitancy, nighttime urination and incontinence.

Neurologist — Physician who specializes in the diagnosis and treatment of conditions related to the nervous system.

Neurology — Study of the nervous system.

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

Neuropsychologist — A psychologist with specialized training in the evaluation of cognitive functions. Neuropsychologists use a series of tests to assess specific cognitive functions and identify cognitive impairment. They also provide treatment for individuals with multiple sclerosis-related cognitive impairment.

Nocturia — The need to urinate during the night.

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

Occupational therapist (OT) — Professionals who assess functioning in everyday activities that are essential for independent living, including dressing, bathing, grooming, meal preparation, writing and driving. An OT can recommend treatments for fatigue management, upper body strength, movement and coordination, adapting the home and work environment and compensating for impairments in thinking, sensation or vision.

Oligoclonal bands — A diagnostic sign indicating abnormal levels of certain antibodies in the cerebrospinal fluid compared with the blood; seen in approximately 90 percent of people with typical multiple sclerosis, but can also be seen in people who don't have multiple sclerosis.

Oligodendrocyte — A type of cell in the central nervous system that's responsible for making and supporting myelin. Myelin is the soft coating surrounding nerve fibers.

Ophthalmoscope — An instrument used to examine the interior of the eye.

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 atrophy can be seen as a result of optic neuritis.

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 (visual) nerve with temporary or permanent impairment of vision and occasionally pain.

Orthotic — A mechanical appliance such as a leg brace or splint that's designed to control, correct or compensate for impaired limb function. Also called orthosis.

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

Paralysis — Inability to move a part of the body.

Paraparesis — A weakness but not total paralysis of the legs.

Paraplegia — Paralysis of both legs.

Paresis — Partial or incomplete paralysis of a part of the body.

Paresthesia — A spontaneously occurring sensation of burning, prickling, tingling or creeping on the skin.

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 appears suddenly, apparently in response to some kind of movement or sensory stimulation, lasts for a few moments and then subsides. People who have paroxysmal symptoms tend to have them often, and they follow a similar pattern from one episode to the next. Examples include 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). Multiple sclerosis relapses are typically not associated with paroxysmal symptoms, but paroxysmal symptoms may be symptoms that are left over after a relapse.

Pediatric nurse practitioner (PNP) — A advanced practice nurse who provides health care to children from birth through 21 years of age, and in specific situations, to individuals older than 21 years old. PNPs provide assessment, diagnosis, management and evaluation of care. The PNP may consult with, and make referrals to, other members of the health care team.

Peripheral nervous system (PNS) — Consists of all of the nerves in the body, outside the central nervous system (CNS), that carry signals from the CNS to the muscles and organs as well as signals from the body into the CNS.

Periventricular region — The area surrounding the four fluid-filled cavities (ventricles) within the brain. Multiple sclerosis plaques are commonly found within this region.

Physiatrist — Physicians who specialize in physical medicine and rehabilitation of physical impairments.

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

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 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. This is frequent in multiple sclerosis.

Plaque — An area of inflamed or demyelinated central nervous system tissue that is characteristic of multiple sclerosis. Also called a lesion.

Plasma cell — A mature B-cell (a type of white blood cell) that produces antibodies. See also Lymphocyte.

Plasmapheresis — Removal of plasma, or the fluid portion of the blood that does not include cells, from the blood. This fluid contains antibodies and its removal is an experimental treatment for multiple sclerosis.

Position sense — The ability to tell, with one's eyes closed, where fingers and toes are in space. Also called proprioception. Position sense is evaluated during the standard neurologic exam in multiple sclerosis.

Postural tremor — Rhythmic shaking that occurs when the muscles are tensed to hold an object or stay in a given 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 multiple sclerosis.

Prevalence — The number of all new and old cases of a disease in a defined population at a particular point in time.

Primary progressive MS — A course of multiple sclerosis characterized from the beginning by progressive worsening, with no remissions.

Prognosis — Prediction of the future course of a disease.

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

Prospective memory — The ability to remember an event or commitment scheduled for the future. People with multiple sclerosis-related memory impairment frequently report problems with this type of memory for remembering upcoming appointments.

Pseudo-bulbar affect — See Affective release.

Pseudo-exacerbation — A temporary aggravation of disease symptoms, resulting from an elevation in body temperature or other stressor such as an infection, severe fatigue or constipation, which disappears once the stressor is removed. A pseudo-exacerbation involves symptom flare-up rather than new disease activity or progression. Pseudo-exacerbation typically doesn't require steroid therapy.

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.

Quadriplegia — The paralysis of both arms and both legs.

Recent memory — The ability to remember events, conversations and content of reading material or television programs from a short time ago. People with multiple sclerosis-related memory impairment typically experience greatest difficulty with recent memory.

Reflex — An involuntary response of the nervous system to a stimulus. Increased, diminished or absent reflexes can indicate neurologic damage, including multiple sclerosis, and reflexes are tested as part of the standard neurologic exam.

Relapsing-remitting MS — A course of multiple sclerosis that's characterized by clearly defined, acute attacks with full or partial recovery and no disease progression between attacks.

Remission — 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 multiple sclerosis tend to experience few, if any, problems with their remote memory.

Remyelination — The repair of damaged myelin. Myelin repair occurs spontaneously in multiple sclerosis but very slowly, and often only partially.

Residual urine — Urine that remains in the bladder following urination.

Retrobulbar neuritis — See Optic neuritis.

Romberg's sign — The inability to maintain balance in a standing position with feet and legs drawn together and eyes closed; related to an impairment in proprioception.

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; related to cerebellar impairment. Also called explosive or ataxic speech.

Sclerosis — Hardening of tissue. In multiple sclerosis, sclerosis is the body's replacement of lost myelin around cells of the central nervous system with scar tissue.

Scotoma — A gap or blind spot in the visual field.

Secondary progressive MS — A course of multiple sclerosis that begins as relapsing-remitting and then becomes progressive at a variable rate, possibly with an occasional relapse and minor remission.

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

Short-term memory — The ability to hold information for a short period of time. For example, remembering a locker combination in the first 20 minutes after it's assigned.

Sign — An objective physical problem or abnormality identified by the health care provider during the neurologic examination. Neurologic signs may differ significantly from the symptoms reported by the patient because they're identifiable only with specific tests and may cause no obvious symptoms. Common neurologic signs in MS include altered eye movements and other changes in the appearance or function of the visual system, altered reflexes, weakness, spasticity and circumscribed sensory changes.

Somatosensory evoked potential (SSEP) — 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, and this test can confirm the presence of a suspected lesion or identify the presence of an unsuspected lesion that has produced no symptoms.

Spasticity — Abnormal increase in muscle tone, manifested as a spring-like resistance to moving or being moved.

Speech/language pathologist — A professional who specializes in the diagnosis and treatment of speech and swallowing disorders. A person with multiple sclerosis may be referred to a speech/language pathologist for help with one or both of these problems. Speech/language pathologists also provide cognitive rehabilitation for persons with cognitive impairment.

Sphincter — A circular band of muscle fibers that tightens or closes a natural opening of the body, such as the external anal sphincter, which closes the anus, and the internal and external urinary sphincters, which close the urinary canal.

Spinal tap — See Lumbar puncture.

Spontaneous voiding — See Incontinence.

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

Steroids — See Corticosteroid or Glucocorticoid hormones.

Suppressor T-lymphocytes — White blood cells that act as part of the immune system and decrease part of the immune system response.

Symptom — A 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.

T-cell — A lymphocyte, a type of white blood cell, that's part of the body's immune system.

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.

Titubation — A form of tremor, resulting from demyelination in the cerebellum, which appears primarily in the head and neck.

Tonic seizure — An intense spasm that lasts a few minutes and affects one or both limbs on one side of the body. These spasms can occur abruptly and fairly frequently, and are similar from one episode to the next. The attacks may be triggered by movement or occur spontaneously, and may require treatment with anti-epileptic medications. Seizures are rare in multiple sclerosis. See Paroxysmal symptom.

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, causing paralysis and numbness in the legs and trunk below the level of the inflammation. This can be associated with bowel or bladder dysfunction.

Tremor — Rhythmic, involuntary movements involving the arms, legs or head, occurring in numerous illnesses and conditions and greatly varying in type and severity.

Trigeminal neuralgia — Lightning-like, acute pain in the face caused by demyelination of nerve fibers where the sensory (trigeminal) nerve root for that part of the face enters the brainstem.

Urinary frequency — Feeling the urge to urinate even when you have urinated very recently.

Urinary hesitancy — The inability to urinate even though you feel the urge to do so.

Urinary incontinence — See Incontinence.

Urinary sphincter — The muscle closing the urethra. Flaccid paralysis of the urinary sphincter causes urinary incontinence, while spastic paralysis results in inability to urinate.

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

Urodynamic testing — Specialized diagnostic tests of the bladder that measure function of the urinary system.

Urologist — A doctor who specializes in urology, the branch of medicine concerned with the male and female urinary tract as well as the male reproductive organs.

Urology — A medical specialty that deals with disturbances of the urinary tract and male reproductive organs.

Vertigo — A dizzying sensation of the environment spinning, often accompanied by nausea and vomiting.

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 neurologic exam.

Visual acuity — Clarity of vision, measured as a fraction of normal vision. A score of 20/20 on a visual acuity test 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 (VEP) — A test in which the brain's electrical activity in response to visual stimuli, such as a flashing checkerboard, is recorded by an electroencephalograph and analyzed by computer. Demyelination results in a slowing of response time. Because this test can confirm the presence of a suspected optic nerve lesion and identify unsuspected lesions, it's extremely useful in diagnosing multiple sclerosis.

Visual processing — The ability to recognize and remember information that you see. For instance, copying notes from the chalkboard or processing what you see on slides or in videos.

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.