Contemporary diagnostic visual and automated polysomnographic REM sleep without atonia thresholds in isolated REM sleep behavior disorder.

Accurate diagnosis of isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is crucial due to its injury potential and neurological prognosis. We aimed to analyze visual and automated REM sleep without atonia (RSWA) diagnostic thresholds applicable in varying clinical presentations in a contemporary cohort of iRBD patients using submentalis (SM) and individual bilateral flexor digitorum superficialis (FDS) and anterior tibialis (AT) electromyography limb recordings during polysomnography. We analyzed RSWA in 20 patients with iRBD and 20 age-REM apnea-hypopnea index matched controls between 2017-2022 for phasic burst durations, density of phasic, tonic, and "any" muscle activity (number of 3-second mini-epochs containing phasic or tonic muscle activity divided by the total number of REM sleep 3-second mini-epochs), and automated Ferri REM atonia index (RAI). Group RSWA metrics were comparatively analyzed. Receiver operating characteristic curves determined optimized area under the curve (AUC) and maximized specificity and sensitivity diagnostic iRBD RSWA thresholds. All mean RSWA metrics were higher in iRBD patients than controls (p<0.05), except for selected AT measures. Optimized, maximal specificity AUC diagnostic cutoffs for co-primary outcomes were: SM "any" 6.5%, 14.0% (AUC=92.5%) and combined SM+FDS "any" 15.1%, 27.4% (AUC=95.8%), while SM burst duration were 0.72 seconds, 0.72 seconds (AUC 90.2%), and FDS RAI 0.930, 0.888 (AUC 92.8%). This study provides evidence for current quantitative RSWA diagnostic thresholds in chin and individual four limb muscles applicable in different iRBD clinical settings and confirms the key value of SM or SM+FDS to assure accurate iRBD diagnosis. Evolving iRBD recognition underscores the necessity of continuous assessment with future large prospective well-harmonized multicenter polysomnographic analyses.

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