Amyotrophic lateral sclerosis (a-mi-o-TROE-fik LAT-ur-ul skluh-ROE-sis), or ALS, is a nervous system (neurological) disease that causes muscle weakness and impacts physical function.
ALS is often called Lou Gehrig's disease, after the famous baseball player who was diagnosed with it. ALS is a type of motor neuron disease that causes nerve cells to gradually break down and die. In the United States, ALS is sometimes called motor neuron disease.
In most cases, doctors don't know why ALS occurs. A small number of cases are inherited.
ALS often begins with muscle twitching and weakness in an arm or leg, or sometimes with slurring of speech. Eventually, ALS can affect your ability to control the muscles needed to move, speak, eat and breathe. ALS can't be cured and eventually leads to death.