Abstract
Chronic fatigue syndrome and fibromyalgia are relatively common clinical syndromes. There are diagnostic criteria for each condition, though fatigue and chronic pain are frequent in both conditions, suggesting possible overlap in their etiopathogenesis. The cause of these conditions remains unknown, and specific, highly successful therapies are not available. Indeed, the heterogeneity of these conditions suggest that the causes are likely multifactorial, and many theories have been offered, mainly involving infectious agents and psychological factors. Some evidence suggests that these disorders may represent disorders of the stress system, comprising the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic nervous system.
