JOHNS HOPKINS HOSPITAL: CLICK TO READ MORE"Multiple sclerosis (MS) is a disorder characterized by destruction of the protective outer casings of the nerves within the central nervous system (the brain, optic nerves, and spinal cord). The nerve casings, known as myelin sheaths, are composed mostly of fats; they insulate the nerves and preserve the speed of electrical transmissions. In MS, patchy areas of the sheaths are destroyed (demyelinated) and replaced by scar tissue (called plaques)-a process known as sclerosis-at multiple sites throughout the central nervous system (hence the name of the disorder). Sclerosis impairs electrical conduction, thus reducing or eliminating transmission of nerve impulses within the affected areas. When severe, the disease may destroy the inner cables of the nerves (axons), causing irreversible damage.

Symptoms wax and wane unpredictably and vary widely from patient to patient. For example, sclerosis of the optic nerves may cause vision disturbances, and sclerosis of the nerves that control the muscles may lead to spasticity, weakness, muscle spasms, or paralysis. Different symptoms may occur in combination and may vary greatly over time.

The initiating cause is unknown; however, current research indicates that MS is an autoimmune disorder, in which the immune system attacks some of the body's own cells, mistaking them for foreign invaders. MS is rare in children and in people over 60; the first episode usually occurs between the ages of 20 and 50.

MS occurs in two major forms. In relapsing/ remitting MS, which afflicts about 70 percent of MS patients, a series of flare-ups or attacks are separated by periods of normal or near-normal health. Such remissions may be short or may last for months or years. In a few cases, remission is permanent, but many patients gradually accumulate permanent neurological deficits.

The other type of MS, chronic/progressive, gradually worsens without remission. Rarely is progression so rapid or severe that survival is limited to only months or a few years. Women are affected more often than men. Average survival after diagnosis is more than 35 years, but destruction of the myelin sheaths eventually results in a combination of nerve, muscle, and, occasionally, brain damage. However, many people retain much of their function for years and are able to pursue a wide range of normal activities with the help of supportive therapy. Current treatment is aimed at reducing the frequency and severity of attacks, relieving the problems caused by neurological deficits, and providing psychological support."