Most experts estimate that there are 300,000 to 400,000 Americans with MS. About 200 new cases are diagnosed each week.

Myelin is the fatty covering that protects the nerve cell fibers in the brain and spinal cord. MS can damage the neurons, but it mostly attacks myelin. Myelin is important because it keeps messages flowing between the brain, spinal cord, and the rest of the body. When MS destroys the myelin, these messages may be slowed or even completely blocked. "Sclerosis" comes from the Greek word for "scarring" or "hardening" of the patchy areas of the CNS where the myelin has been destroyed.

Women develop MS nearly twice as often as do men. Whites are more than twice as likely to develop MS as are other racial groups. People who live in temperate climates are more than 5 times as likely to develop MS as are people who live in tropical areas.

MS is considered an autoimmune disease. This means the body's immune system attacks the body's own tissues. Because MS is so much more common in temperate climates than in tropical ones, researchers think the environment may have an effect. Some researchers guess that there may be something protective that people in the tropics are able to acquire. Viruses also may play a role in MS. MS often grows worse after an acute viral illness, the NINDS says. Genes may also play a role. The risk of developing MS also goes up a bit if a family member has the disease.

There are different forms of MS: * Relapse-remitting MS. The disease begins with a series of attacks, with periods of remissions that last 1 to 2 months. This is the most common form of MS. * Primary-progressive MS. The person's function gradually gets worse, with no remissions, the NINDS says. It can lead to paralysis. * Secondary-progressive MS. This form begins with relapses and remissions and then becomes progressive. This affects about half of those with relapse-remitting MS. * Progressive-relapsing MS. This is progressive, with acute attacks. It is rare. * About 1 in 5 people with MS have a mild form of the disease that does not get worse.

Researchers think that this temporary remission is related to changes in a woman's immune system during pregnancy. Up to 2 in 5 women with MS have a relapse of symptoms within 3 months of delivery. Women with MS who are planning a family should talk with their healthcare provider about medicines they use for MS. Certain medicines should not be taken during pregnancy and while breastfeeding. These medicines may cause birth defects. Check with your provider for a list of these medicines.

Eye problems linked to MS also include red-green color distortion and blindness in one eye, the NINDS says. These eye problems tend to ease in later stages of MS. Muscle weakness can be so severe that the person has problems walking or standing. Other symptoms include numbness, prickling, speech problems, tremors, dizziness, loss of bowel or bladder control, difficulty concentrating, memory problems, and sometimes hearing loss.

MRI is an imaging test that uses a magnetic field, radio waves, and a computer to makes pictures of internal body structures. Spinal tap (lumbar puncture) is used to test the cerebrospinal fluid for signs of MS. These tests can help find plaques in the brain that may mean MS. Visual evoked potential tests measure the speed of the brain's response to various visual signals and may find lesions and plaques that the scanning techniques may have missed, the NINDS says. No single lab test can diagnose MS.

Although corticosteroids and the hormone ACTH are given to people with an acute attack of MS, those with slowly progressing MS don't always do better if they take these medicines daily. Newer medicines have been developed that can modify the effects of MS. Healthcare providers will tailor their advice for treatment based on the person's situation. There is no cure for MS.

Many quack cures have emerged for MS over the years. None of the "cures" on the list work and some may be dangerous. Other so-called treatments include electrical stimulation of the spinal cord, removal of the thymus gland, and beef heart and pig pancreas extracts, the NINDS says.