Multiple sclerosis (MS) is a chronic, potentially debilitating disease that affects your central nervous system, which is made up of your brain and spinal cord. Multiple sclerosis is widely believed to be an autoimmune disease, a condition in which your immune system attacks components of your body as if they’re foreign.

In multiple sclerosis, the body mistakenly directs antibodies and white blood cells against proteins in the myelin sheath, a fatty substance that insulates nerve fibers in your brain and spinal cord. This results in inflammation and injury to the sheath and ultimately to the nerves that it surrounds. The result may be multiple areas of scarring (sclerosis). Eventually, this damage can slow or block the nerve signals that control muscle coordination, strength, sensation and vision.

Multiple sclerosis is unpredictable and varies in severity. In some people, multiple sclerosis is a mild illness, but it can lead to permanent disability in others. Treatments can modify the course of the disease and relieve symptoms.