An autoimmune disorder of the central nervous system (brain and spinal cord). Nerve cells normally are surrounded by an insulating sheath made of a fatty substance called myelin that helps to transmit nerve impulses. In MS, this myelin sheath is inflamed or damaged. This disrupts or slows nerve impulses and causes nerves to malfunction. Scarring (sclerosis) occurs in the white matter of the brain and spinal cord. These areas of myelin damage and scarring are called MS plaques. The disease periodically flares up with episodes of increased symptoms. The disease can be mild, and non-progressive disease, can slowly get worse, or get worse rapidly. It is slightly more common in women between the ages of 20 to 40.