Polysomnographic phenotype of isolated REM sleep without atonia

•Rapid eye movement (REM) density is increased in isolated REM sleep without atonia (RSWA).•Periodic limb movements of sleep are increased in isolated RSWA.•Heart rate variability is normal in isolated RSWA. Isolated REM sleep without atonia (iRSWA) is regarded as a prodromal phase of REM sleep behavior disorder and synucleinopathies. In iRSWA patients, we investigated the polysomnographic characteristics that are known to be altered in (prodromal) Parkinson’s disease (PD): periodic limb movements of sleep [PLMS] (increased), REM density (reduced), and heart rate variability ([HRV] (reduced). We compared video-polysomnographic studies of 49 iRSWA subjects with 41 controls. RSWA and PLMS were scored visually. REM density (REM/hour) and HRV were calculated automatically. We found a higher median total (15.90 vs 7.20; p = 0.001), REM (21.80 vs 11.0; p