A disease in which the immune system breaks down the protective coating of nerve fibers in the brain and spinal cord, called the myelin sheath.

Genetics and environmental factors can increase the risk of multiple sclerosis (MS). Women ages 20 to 40 and people with a family history have a higher risk. Viral infections, some autoimmune diseases, living in temperate climates and having low levels of vitamin D are associated with MS.

Multiple sclerosis (MS) symptoms may include numbness or weakness in one or more limbs. People with MS may be unsteady or unable to walk. MS may cause tingling and an electric-shock feeling when moving the neck forward. It also can cause fatigue and changes in vision.

Medicines that target the body's immune system can help slow the progression of multiple sclerosis and reduce relapses. Physical therapy and medicines help manage symptoms.