| Risk Factors Multiple sclerosis (MS) is a disease of the
central nervous system. It is a chronic condition that can be
disabling. There are several types of MS: Relapsing-remitting
MS—Symptoms suddenly reappear periodically. They last for a few
weeks or months, then go back into remission (a period with no
symptoms). Symptoms may get worse with each occurrence. Primary
progressive MS—Symptoms gradually worsen after symptoms first
appear. Relapses and remissions usually do not occur. Secondary
progressive MS—After years of relapses and remissions, symptoms
suddenly begin to progressively worsen. Progressive relapsing
MS—Symptoms gradually worsen after symptoms first appear. One or
more relapses may also occur. Nerve Fiber (Neuron) Copyright ©
Nucleus Medical Media, Inc. The immune system normally attacks
viruses or bacteria that should not be in the body. With MS, a
problem with the immune system causes it to attack healthy
nerves. In particular, MS attacks the nerve fibers in the brain,
spinal cord, and the