Isolated REM sleep without atonia and isolated REM sleep behaviour disorder: a study of clinical and prognostic...

Isolated REM sleep without atonia (iRSWA) is increasingly detected on polysomnography (PSG), yet its clinical relevance remains unclear. We compared the demographic profile, sleep physiology, comorbidities, and longitudinal outcomes of people with iRSWA and isolated REM sleep behaviour disorder (iRBD).

We retrospectively reviewed PSG reports (2008-2022) from a tertiary sleep-medicine center, classifying people as iRSWA or iRBD based on self-reported dream-enactment behavior. Clinical data were extracted from charts, and PSG variables from sleep reports. Neurological and psychiatric diagnoses before the sleep examination were obtained from national registries. Comparisons used multivariable regression and Fine-Gray competing-risk models.

The cohort comprised 302 participants (iRSWA = 98 and iRBD = 204). Participants with iRSWA were more often female (38.8% vs 23%, p = .004), with a younger age distribution (35-49 years; 25.5% vs 13.7%, p = .015). They reported more daytime sleepiness/fatigue (odds ratio [OR] 2.84, p < .001) despite comparable objective sleep architecture. Objective neurodegenerative signs appeared only in the iRBD group. Pre-index neurological disorders were more common in iRSWA (31.6% vs 19.1%, p = .042), while neurodegenerative conversion during follow-up occurred in 4.1 per cent of iRSWA and 8.8 per cent of iRBD. In multivariable analysis, sleepiness/fatigue and pre-existing neurological disorder were associated with iRSWA; when spouse status was included in the model, spouse status became the strongest predictor, periodic limb movements in sleep of 15 or more reached significance, and the association with sex attenuated.

iRSWA differs from iRBD in profile and pre-index comorbidity patterns. Our findings support the view that iRSWA may reflect mechanisms other than a uniform prodromal stage of α-synucleinopathy.