Rapid eye movement sleep without Atonia in healthy university students without clinical rapid eye movement sleep behavior disorder

Rapid eye movement (REM) sleep without atonia (RWA) on polysomnography (PSG) is an essential finding for the diagnosis of idiopathic REM sleep behavior disorder (RBD). However, there are no internationally agreed criteria for a normative RWA range for young adults to determine if the observed RWA is pathologically significant. We aimed to clarify the rate of RWA by re-evaluating existing PSGs of healthy university students and provide evidence for a normative RWA range in their 20s. This single-center, retrospective study involved re-evaluation of PSG data obtained from 25 healthy university students without clinical RBD for other research purposes between August 2019 and July 2022. For RWA quantification, submentalis muscle electromyography (EMG) activity during REM sleep was determined according to the American Academy of Sleep Medicine scoring manual. Subsequently, the RWA index, defined as the ratio of epochs with phasic or tonic RWA to all epochs during REM sleep was calculated. These indicators were compared between males and females. Of the 25 participants, six were male and 19 were female, with a mean age of 22.7 ± 2.1 years. RWA was observed for > 1 epoch in 88.0% participants; phasic EMG activity was 2.5% ± 2.5%, tonic EMG activity was 0.3% ± 0.5%, and RWA index was 2.8% ± 2.7%. No participants exceeded the conventional pathological cutoff value. The phasic and tonic RWA durations were 1.6 ± 1.0 s and 22.6 ± 6.0 s, respectively. The maximum amplitudes of the phasic and tonic RWAs were 191.8 ± 144.8 µV and 191.8 ± 242.4 µV, respectively. Only the phasic RWA duration showed a significant sex difference (p = 0.0323). There were no significant sex differences in the other indicators. 88% of healthy university students without clinical RBD could identify at least one epoch of muscle activity during REM sleep and the RWA index was 2.8%. This result contributes to the establishment of a normative RWA range for healthy young adults in their 20s.