The cause of this disorder is unknown. Physical or emotional trauma may play a role in development of the syndrome. Some evidence suggests that fibromyalgia patients have abnormal pain transmission responses. It has been suggested that sleep disturbances, which are common in fibromyalgia patients, may actually cause the condition. Another theory suggests that the disorder may be associated with changes in skeletal muscle metabolism, possibly caused by decreased blood flow, which could cause chronic fatigue and weakness. Others have suggested that an infectious microbe, such as a virus, triggers the illness. At this point, no such virus or microbe has been identified. Pilot studies have shown a possible inherited tendency toward the disease, though evidence is very preliminary. The disorder has an increased frequency among women 20 to 50 years old. The prevalence of the disease has been estimated between 0.7% and 13% for women, and between 0.2% and 3.9% for men.
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