Multiple sclerosis (MS) involves an immune-mediated process in which an abnormal response of the body’s immune system is directed against the central nervous system (CNS), which is made up of the brain, spinal cord and optic nerves. The exact antigen — or target that the immune cells are sensitized to attack — remains unknown, which is why MS is considered by many experts to be “immune-mediated” rather than “autoimmune.”
Within the CNS, the immune system attacks myelin — the fatty substance that surrounds and insulates the nerve fibers — as well as the nerve fibers themselves.
The damaged myelin forms scar tissue (sclerosis), which gives the disease its name.
When any part of the myelin sheath or nerve fiber is damaged or destroyed, nerve impulses traveling to and from the brain and spinal cord are distorted or interrupted, producing a wide variety of symptoms.
The disease is thought to be triggered in a genetically susceptible individual by a combination of one or more environmental factors.
People with MS typically experience one of four disease courses, which can be mild, moderate or severe.