Circadian rhythms of women with fibromyalgia

Fibromyalgia syndrome is a chronic and debilitating disorder characterized by widespread nonarticular musculoskeletal pain whose etiology is unknown. Many of the symptoms of this syndrome, including difficulty sleeping, fatig ue, malaise, myalgias, gastrointestinal complaints, and decreased cognitive function, are similar to those observed in individuals whose circadian pac emaker is abnormally aligned with their sleep-wake schedule or with local e nvironmental time. Abnormalities in melatonin and cortisol, two hormones wh ose secretion is strongly influenced by the circadian pacemaker, have been reported in women with fibromyalgia. We studied the circadian rhythms of 10 women with fibromyalgia and 12 control healthy women. The protocol control led factors known to affect markers of the circadian system, including ligh t levels, posture, sleep-wake state, meals, and activity. The timing of the events in the protocol were calculated relative to the habitual sleep-wake schedule of each individual subject. Under these conditions, we found no s ignificant difference between the women with fibromyalgia and control women in the circadian amplitude or phase of rhythms of melatonin, cortisol, and core body temperature. The average circadian phases expressed in hours pos thabitual bedtime for women with and without fibromyalgia were 3:43+/-0:19 and 3:46+/-0:13, respectively, for melatonin; 10:13+/-0:23 and 10:32+/-0:20 , respectively for cortisol; and 5:19+/-0:19 and 4:57+/-0:33, respectively, for core body temperature phases. Both groups of women had similar circadi an rhythms in self-reported alertness. Although pain and stiffness were sig nificantly increased in women with fibromyalgia compared with healthy women , there were no circadian rhythms in either parameter. We suggest that abno rmalities in circadian rhythmicity are not a primary cause of fibromyalgia or its symptoms.