Absence of dysregulation in amplitude and phase of circadian rhythm of core body temperature in idiopathic hypersomnia: A case-control study.

Study objectives: To investigate amplitude and phase of the circadian rhythm of core body temperature (CBT) via the continuous measure of the gastrointestinal temperature in participants with idiopathic hypersomnia (IH), non-specified hypersomnia (NSH) compared to healthy controls (HC) in a constant routine standardized bedrest (BR) protocol.

Methods: Consecutive participants evaluated in a National Reference Center for Rare Hypersomnias benefited from an extensive evaluation with one night polysomnography, followed by modified Multiple Sleep Latency Test (mMSLT), and a continuous 32-hour BR recording in standardized conditions. CBT was recorded via a telemetry pill (e-Celsius®) during the BR, modeled by a Cosinor, with extraction of MESOR, amplitude and phase. Participants with IH, diagnosed according to ICSD-3, were compared with participants with NSH (complaint of hypersomnolence but normal mMSLT and BR), and HC. Participants were divided in 4 groups based on their mMSLT mean sleep latency (mMSLT+,≤8min) and their BR total sleep time (BR+,≥19h).

Results: 108 participants (80% women, 28.3±7.8 y.o) were included in the analyses, 81 IH (83% women), 16 NSH (75% women), 11 HC (64% women). Cosinor amplitude and phase of CBT did not differ between IH, NSH and HC, nor in the subgroup analysis (37 BR+/mMSLT+, 35 BR+/mMSLT-, 9 BR-/mMSLT+, 27 BR-/mMSLT-). No difference in chronotypes was observed between groups. Women had a greater MESOR and reduced CBT amplitude compared to men.

Conclusion: The circadian rhythm of CBT showed no difference in amplitude or phase between IH, NSH and HC, and was not related to prolonged sleep time or objective daytime sleepiness.