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What Is It?

Multiple sclerosis (MS) is a disabling neurological illness. It affects the brain and spinal cord. The disease is usually progressive. This means it worsens over time.

An insulating sheath called myelin normally surrounds nerve cells. Myelin helps to transmit nerve impulses.

In MS, the myelin sheath becomes inflamed or damaged. This disrupts or slows nerve impulses. The inflammation leaves areas of scarring called sclerosis.

Multiple sclerosis may also damage nerve cells, not just their myelin lining.

The disruption of nerve signals causes a variety of symptoms. MS can affect a person's vision, ability to move parts of the body, and ability to feel sensations (such as pain and touch).

Symptoms usually come and go. Periods when symptoms suddenly get worse are called relapses. They alternate with periods when symptoms improve, called remissions.

Many people have a long history of MS attacks over several decades. In these cases, the disease may worsen in "steps," when the attacks occur. For others, the disease worsens steadily. In a minority of patients, MS causes relatively few problems.

Scientists believe MS is an autoimmune disease. This means the immune system mistakenly attacks its own body. In this case, the body attacks the myelin sheaths of the nerves.

Several viruses have been linked to MS. But they are not proven causes of the disease. Fever, other physical or emotional stress may contribute to a flare-up of symptoms. The timing, duration and damage of MS attacks are unpredictable.

The symptoms of MS usually begin before age 40. But people between ages 40 and 60 sometimes are affected. Having a close relative with MS increases your chances of developing the disease.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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