Fibromyalgia (FM) and chronic fatigue syndrome (CFS) are stress associated disorders mainly affecting women. FM is characterized primarily by widespread musculoskeletal pain, and CFS by profound debilitating fatigue, but there is considerable overlap of clinical symptoms between these 2 syndromes. Neuroendocrine abnormalities have been noted in both FM and CFS and desynchronization of circadian systems has been postulated in their etiology. The pineal hormone melatonin is involved in synchronizing circadian systems and the use of exogenous melatonin has become widespread in patients with FM and CFS.
We examined the characteristics and relationship of melatonin and cortisol levels in premenopausal women with FM (n = 9) or CFS (n = 8), compared to age and menstrual cycle phase matched controls. Blood was collected from an indwelling intravenous catheter every 10 min over 24 h, and plasma melatonin and cortisol were determined by radioimmunoassay at 60 and 10 min intervals, respectively.
Night time (23:00-06:50) plasma melatonin levels were significantly higher in FM patients compared to controls (p<0.05), but there was no significant difference in melatonin levels between CFS patients and controls. No differences in the timing of cortisol and melatonin secretory patterns and no internal desynchronization of the 2 rhythms were found in either patient group, compared to controls.
Raised plasma melatonin concentrations have been documented in several other conditions that are associated with dysregulation of neuroendocrine axes. Increased melatonin levels may represent a marker of increased susceptibility to stress induced hypothalamic disruptions. These data indicate that there is no rationale for melatonin replacement therapy in patients with FM and CFS.