Circadian rhythm of core body temperature in subjects with chronic fatiguesyndrome

The pathophysiological basis for chronic fatigue syndrome (CFS) remains poo rly understood. Certain symptoms of CFS, namely fatigue, neurocognitive sym ptoms and sleep disturbance, are similar to those of acute jet lag and shif t work syndromes thus raising the possibility that CFS might be a condition associated with disturbances in endogenous circadian rhythms. In this stud y, we tested this hypothesis by examining the circadian rhythm of core body temperature (CBT) in CFS and control subjects. Continuous recordings of CB T were obtained every 5 min over 48 h in a group of 10 subjects who met the Center for Disease Control (CDC) definition of CFS and 10 normal control s ubjects. Subjects in the two groups were age, sex and weight-matched and we re known to have normal basal metabolic rates and thyroid function. CBT rec ordings were performed under ambulatory conditions in a clinical research c entre with the use of an ingestible radio frequency transmitter pill and a belt-worn receiver-logger. CBT time series were analysed by a cosinor analy sis and by a harmonic-regression-plus-correlated model to estimate the mean , amplitude and phase angle of the rhythm. The goodness of fit of each mode l was also compared using the Akaike Information Criterion (AIC) and sigma (2). Average parameters for each group were compared by Student's t-test. B y cosinor analysis, the only significant difference between CFS and control groups was in the phase angle of the third harmonic (P = 0.02). The optima l harmonic-regression-plus-correlated-noise models selected were ARMA(1,1): control 7, CFS 6; ARMA(2,0): control 1, CFS 4; and ARMA(2,1): control 2 su bjects. The optimal fit ARMA model contained two harmonics in eight of 10 c ontrol subjects but was more variable in the CFS subjects (1 harmonic: 5 su bjects; 2 harmonics: 1 subject; 3 harmonics: 4 subjects). The goodness of f it measures for the optimal ARMA model were also better in the control than the CFS group, but the differences were not statistically significant. We conclude that, measured under ambulatory conditions, the circadian rhythm o f CBT in CFS is nearly indistinguishable from that of normal control subjec ts although there was a tendency for greater variability in the rhythm. Hen ce, it is unlikely that the symptoms of CFS are because of disturbance in t he circadian rhythm of CBT.