Overview

Multiple Sclerosis (MS) is a chronic neurological disease that affects the nerve cells in the brain and spinal cord. Under normal circumstances, nerve impulses throughout the body pass along nerve fibers, which connect to one another at synapses. A fatty substance called myelin insulates the nerve fibers and facilitates the smooth transmission of high-speed messages between the brain, the spinal cord and the rest of the body.

Damage to any part of the myelin sheath disrupts the messages that are being transmitted within the body. In MS, misguided cells of the central nervous system destroy areas of myelin. As a result, myelin becomes inflamed and swollen, leaving scar tissue called sclerosis. Sometimes the nerve fiber itself is damaged. With damaged myelin and nerve tissue, the nerve fibers cannot conduct electrical impulses to and from the brain as well. This produces the various symptoms of multiple sclerosis.

Most people with multiple sclerosis are diagnosed between the ages of 16 and 40, but some people are affected earlier and others do not get their first symptoms until age 60. It is estimated that in the United States, 250,000 to 350,000 people have MS, and each year about 10,400 people are newly diagnosed.

Multiple sclerosis affects women almost twice as frequently as men. Caucasians are more than twice as likely as African-Americans or Hispanics to get the disease. The disease is relatively rare among those of Asian descent.

The disease is more common in temperate climates -- like those in the northern United States, Canada and Europe -- than in tropical regions. The fact that MS is more prevalent in certain climates leads researchers to speculate that environmental factors play a role in the development of MS. Research in this area has yet to provide conclusive evidence of a direct link between the environment and MS.

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This article was reviewed and updated June 2007.