Multiple sclerosis, often called MS, is a disease that affects the central nervous system-the brain and spinal cord. It can cause problems with muscle control and strength, vision, balance, feeling, and thinking.

Your nerve cells have a protective covering called myelin. Without myelin, the brain and spinal cord can't communicate with the nerves in the rest of the body. MS gradually destroys myelin in patches throughout the brain and spinal cord, causing muscle weakness and other symptoms. These patches of damage are called lesions.  WebMD