Polysomnographic phenotype of isolated REM sleep without atonia

Abstract Objective 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). Methods 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. Results We found a higher median total (15.90 vs 7.20;p=0.001), REM (21.80 vs 11.0;p Conclusions Our results suggest an association between RWSA and REM density and PLMS, but not HRV. The positive correlation between these variabilities may imply overlapping pathophysiological processes. Significance The evidence of higher REM density and normal HRV weakens the hypothesis that iRWSA is a prodromal PD stage. An alternative interpretation is, however, that REM density and HRV change during caudal-rostral neurodegeneration.