"Amyotrophic" refers to a loss of muscle mass; "Lateral" refers to the nerve tracks that run down both sides of the spinal cord, where many neurons affected by ALS are found; "Sclerosis" refers to the scar tissue that remains after disintegration of nerves occurs.
Dr. Jean-Martin Charcot, a French neurologist, first described ALS in 1869. He was the first physician to link symptoms of ALS to a group of nerves specifically affected by the disease - the motor neurons that originate in the spinal cord.
It is difficult to diagnose ALS because it resembles other diseases, such as primary lateral sclerosis, progressive bulbar palsy, progressive muscular atrophy, and progressive pseudo bulbar palsy. There appear to be two main types of ALS in the general population: Familial Approximately 5-10 percent of ALS cases are familial. Of those cases, 20 percent have a genetic defect in a specific chromosome; Sporadic About 90 percent of cases have no definitive cause.
Worldwide, the annual incidence of ALS is 2.5 new cases per 100,000 people. It is estimated that approximately 25-30,000 people have ALS in the USA.