After osteoarthritis, fibromyalgia is the second most common 'rheumatic' disorder. Depending on the diagnostic criteria used, the prevalence is from 2% to 8% of the population."
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Patients with fibromyalgia are likely to have a history of headaches, dysmenorrhea, temporomandibular joint disorder, chronic fatigue, irritable bowel syndrome and other functional gastrointestinal disorders,interstitial cystitis/painful bladder syndrome, endometriosis, and other regional pain syndromes (especially back and neck pain)."

Source : Fibromyalgia : A Clinical Review, Clinical Crossroads, April 16, 2014

The cause(s) of Fibromyalgia are unknown. Hypotheses include environmental, psychological, and genetic factors, as well as auto-inflammatory responses. There is also a theory which suggests "central sensitization" (see: Fibromyalgia: A Clinical Update Evidence-Based Clinical Review, September 2013)

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