Multiple sclerosis (MS) is a chronic (long-term), progressive, degenerative disorder that affects nerve fibers in the brain and spinal cord. Multiple sclerosis is widely believed to be an autoimmune disease, a condition in which the immune system attacks components of the body as if they are foreign.
A fatty substance, called myelin, surrounds and insulates nerve fibers and facilitates the conduction of nerve impulse transmissions. MS is characterized by damage to myelin (called demyelination) caused by the destruction of specialized cells (oligodendrocytes) that form the myelin. Demyelination causes scarring and hardening (sclerosis) of nerve fibers usually in the spinal cord, brain stem, and optic nerves, which slows nerve impulses and results in weakness, numbness, pain, and vision loss.
Because different nerves are affected at different times, MS symptoms often worsen, improve, and develop in different areas of the body. Early symptoms of the disorder may include vision changes, such as blurred vision or blind spots, and muscle weakness.
MS can progress steadily or cause acute attacks (exacerbations) followed by partial or complete reduction in symptoms (remission). Most individuals with the disease have a normal lifespan.
MS affects over 250,000-500,000 people in the United States and may affect 2.5 million people worldwide. Northern Europe and the northern United States have the highest prevalence, with more than 30 cases per 100,000 people. Multiple sclerosis affects two to three times as many women as men, and affects Caucasians more often. Most individuals experience their first signs or symptoms between ages 20 and 40. Children of parents with MS have a higher rate of incidence (30-50%). Heredity does play a role in the development of MS.
Multiple sclerosis is unpredictable and varies in severity. In some individuals, 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.