Core body temperature is normal in chronic fatigue syndrome

Background: Subjects with chronic fatigue syndrome (CFS) frequently report symptoms of subnormal body temperature and low-grade fever. We conducted a study to determine whether CFS subjects manifest any abnormality of core body temperature (CBT) that might help explain their fatigue. Methods: Continuous 24-hour recordings of CBT measured every 5 min were performed in 7 subjects meeting the Centers for Disease Control definition of CFS. Three additional groups were studied: normal controls, subjects with seasonal allergy, and subjects with major depression. Subjects (n = 7) in each group were age-, sex-, and weight-matched to the CFS group and had normal basal metabolic rates, thyroid function, and 24-hour urinary free cortisol excretions. CTB was measured with an ingestible radio frequency transmitter pill and a belt-worn receiver-logger. Each pill was factory-calibrated to ± 0.1°C and field-calibrated with a water bath calibration prior to use. Results: The 24-hour mean calibration-adjusted CBTs of each group were not significantly different (control: 37.00 ± 0.17°C; CFS: 37.04 ± 0.31°C; allergy: 37.15 ± 0.18°C; depression: 37.16 ± 0.18°C). Similarly, the mean peak and trough circadian temperatures were not statistically different. The mean 24-hour profile of CBT for each group showed a similar circadian rhythm. In simultaneously collected blood samples, each group showed a similar circadian profile of serum cortisol with a peak occurring at 08:00. Conclusions: Subjects with CFS have normal CBT despite frequent self-reports of subnormal body temperature and low-grade fever.