Sometimes, knowing what something isn't can be as important as knowing what it is. That's true with fibromyalgia. The symptoms of FMS overlap with so many other maladies that you could be misdiagnosed several times before learning you have fibromyalgia. Getting a better understanding of these other conditions can help you figure out whether you actually have fibromyalgia or something else. This chapter examines six of the most common imitators.