Amyotrophic Lateral Sclerosis - Description

Under normal circumstances, muscles move because of messages sent from the brain through the spinal cord to the muscles. These messages are carried by motor neurons. In ALS, those motor neurons die off and messages from the brain to the muscles do not flow normally. Muscles do not respond when they are supposed to or as well as they should.

The death of motor neurons affects voluntary muscles. These muscles are controlled by conscious thought. They include muscles in the legs, arms, and trunk. These muscles normally move when a person wants them to move. As ALS develops, a person loses that control over these muscles.

ALS normally does not affect other kinds of muscles, such as those in the heart or digestive system. It also has no effect on the brain. Thus, ALS patients can usually think normally, although they lose the ability to move.

ALS affects approximately thirty thousand people in the United States. About five thousand new cases are diagnosed each year. Most cases occur in people between the age of forty and seventy. Men are slightly more likely to develop ALS than women.

ALS usually progresses slowly. In about half of all patients, it causes death within three years. About 80 percent of all patients die in less than five years, and a small number (about 10 percent) survive more than eight years.