Multiple sclerosis (MS) is a chronic neurological disease that involves the central nervous system—specifically the brain, spinal cord, and optic nerves. Relapsing-remitting multiple sclerosis is a form of MS in which symptoms randomly flare up (relapse) and then improve or fade (remission).

This relapsing-remitting pattern emerges with the onset of the disease and may last for many years. MS can cause problems with muscle control and strength, vision, balance, sensation, and mental functions.

The disease does not advance during the remissions, but loss of nerve function that can occur during relapses is permanent. After repeated relapse episodes, the loss of nerve function can cause severe symptoms that do not improve.