Multiple Sclerosis - Definition
Multiple sclerosis (MS; pronounced multiple skluh-RO-siss) is a chronic autoimmune disorder (see autoimmune disorders entry) that affects the nerves. "Chronic" means that it develops slowly over time; "autoimmune" means that the body's immune system becomes confused about some part of the body it is designed to protect. It attacks that part of the body as if it were a foreign invader. MS affects a person's ability to move, to feel, and to control his or her body functions.