FM is usually diagnosed by examining certain points on your body and determining if they are tender. Some researchers and physicians believe this diagnostic criteria is out of date and they will diagnose fibromyalgia by excluding other diseases and determining if you fit the constellation of symptoms associated with the disease. They include in general widespread body pain without redness or swelling, fatigue, reduced ability to think, sensitivity to stimuli such as lights and odors, sometimes sensitivity to touch, etc. It takes an experienced doctor to recognize and diagnose FM.
Check out the fibromyalgia section on Health Central for more information.