Fibromyalgia: chronobiological aspects.

The primary fibromyalgia syndrome (Weichteilrheumatismus) shows a circadian rhythm of the symptoms and, moreover, a seasonality of pain severeness. Although the pathophysiologic mechanisms are unknown, the circadian variations are well documented in the literature; the seasonality of pain is sometimes clinically reported. In a study on "healthy" workers, the seasonality of this disease is reported.