Multiple sclerosis (MS) is a chronic, disabling disease affecting the central nervous system, composed of the brain, spinal cord and optic nerves. The disease affects more than two million people worldwide. MS is thought to be an autoimmune disease, meaning that the body's immune system mistakenly attacks the person's healthy tissues. The underlying cause of the immune system's malfunction in MS patients is not yet understood. In patients with MS, immune system attacks target the protective insulation (myelin) surrounding the nerve fibers of the central nervous system, producing inflammation, destruction and scarring. Scar tissue (sclerosis) forms in place of the myelin and causes a slowing and/or blockage of electrical signals from the brain to other parts of the body. The physical symptoms associated with MS—which vary from person to person, and even from time to time in the same person—are a direct result of this impaired transmission of nerve signals. There is currently no cure for MS, though there are treatments and medications available to help control symptoms and slow the progression of the disease.
MS typically progresses along one of four clinical courses, each of which may be mild, moderate or severe: