ALS definition
Amyotrophic lateral sclerosis (ALS) is a disease that breaks down tissues in the nervous system (a neurodegenerative disease) of unknown cause that affects the nerves responsible for movement. It is also known as motor neuron disease and Lou Gehrig's disease, after the baseball player whose career it ended.myotrophic lateral sclerosis (ALS) (ÄÂ´mÄ«ÉtrÅÂ´fik latÂ´ÉrÉl sklÉrÅÂ´sis) , n a degenerative disease of the motor neurons, characterized by atrophy of the muscles of the hands, forearms, and legs, and spreading to involve most of the body. Colloquial term is Lou Gehrig's disease.