Abstract Introduction Chronic insomnia is diagnosed from the complaint, yet PSG is often used to verify the disorder. In many cases, patients report severe symptoms but show no measurable abnormalities during sleep recordings. This gap between experience and objective data remains poorly explained. REM sleep is particularly sensitive to arousal and may provide insight into this discrepancy. We therefore examined REM microstructure to determine whether it distinguishes insomnia cases with and without PSG-defined abnormalities. Methods Our database of 1049 participants, was composed of 141 good sleepers (GS), 214 insomnia without PSG abnormalities (CIN-NP), and 694 insomnia with PSG abnormalities (CIN-AP). Chronic insomnia was diagnosed by qualified doctors, specialised in sleep, according to the ICSD-3 guidelines. The data was analysed using automated algorithms (GSSC, YASA, MAD), in order to obtain precise scoring of sleep stages, arousals and REM metrics. The Odds Ratio Product (ORP) was also used, in order to quantify arousal dynamics. Results Compared with good sleepers, both insomnia groups exhibited disrupted REM stability. They showed a greater frequency of REM arousals and awakenings, along with increased rapid eye movement activity and a higher proportion of phasic REM. The two insomnia subtypes were largely similar in terms of arousal rates; however, the duration of REM awakenings clearly separated them. CIN-AP had longer awakenings during REM, even though conventional PSG metrics did not differ. Multinomial models showed that CIN-AP was more likely to occur in older males and was characterised by reduced overall REM duration but a larger proportion of REM sleep, together with more phasic REM and prolonged REM awakenings. The classification model reached an AUC of 0.752, and performance improved slightly once ORP and awakening duration were incorporated (AUC 0.755). Conclusion REM sleep behaviour offers a distinct signature for insomnia subtypes. The pattern of instability during REM separates patients with PSG-defined abnormalities from those whose recordings appear normal, and may explain the frequent mismatch between sleep complaints and objective findings. These REM-derived markers provide potential neurophysiological indicators of insomnia and could support more targeted diagnosis and treatment strategies. Support (if any)
Hanif et al. (Fri,) studied this question.