• Joshua Aviram, Tamar Shochat, and Dorit Pud.
• Faculty of Social Welfare and Health Sciences, University of Haifa, Haifa, Israel.
• Pain Med. 2015 Jun 1;16(6):1137-44.

ObjectiveSeveral physiological processes exhibit 24-hour oscillations termed circadian rhythms. Despite numerous investigations on the circadian dynamics of pain perception, findings related to this issue remain inconsistent. This study aimed to assess the effect of time-of-day on multimodal experimental pain perception in healthy males, including "static" and "dynamic" quantitative sensory tests.DesignA random order tests were performed in the morning, afternoon and evening.SubjectsForty-eight healthy males (25.9 ± 4.7 years old).MethodsThree different pain modalities i) mechanical (pain threshold, tolerance, and intensity), ii) heat (pain threshold and intensity), iii) cold (pain threshold measured in °C and in seconds and cold pain tolerance and intensity) utilizing nine "static" pain parameters, and two "dynamic" pain paradigms i) temporal summation and ii) conditioned pain modulation were assessed in each session.ResultsPain scores varied significantly in six pain parameters during the day. Specifically, lower pain scores were found in the morning for cold pain threshold (in seconds and in °C), cold pain intensity, cold pain tolerance, heat pain threshold and intensity. There were no significant diurnal differences in the mechanical evoked pain parameters or in either of the "dynamic" pain paradigms.ConclusionsThermal pain scores varies during the day and morning seems to be the time-of-day most insensitive to pain. Also, dynamic tests and the mechanical pain model are not appropriate for detecting diurnal variability in pain. The results of this study may be partially explained by a potential analgesic effect of some hormones known to have diurnal variation (e.g., melatonin and cortisol).Wiley Periodicals, Inc.

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