MS is an autoimmune disease, when the body's immune system mistakenly attacks its own cells. Doctors do not know exactly why fibromyalgia occurs, but it appears to result from a change in the way a person perceives pain.
The symptoms can be similar, but people with fibromyalgia are more likely to experience depression, irritable bowel syndrome, and widespread, persistent pain. Symptoms more common with MS include weakness, vision problems, muscle spasms, and bowel or bladder issues.