Fibromyalgia is an imprecise, clinically defined syndrome with no histological or other diagnostic abnormalities on investigation, and no known cause. The American College of Rheumatology 1990 diagnostic criteria are widespread pain (both sides of the body, above and below the waist, and spine or anterior chest) together with tenderness at 11 of 18 defined points (Arthritis and Rheumatism 1990;33:160–72). Although it is …