REM sleep microstructure alterations in REM sleep behavior disorder: beyond muscle tone
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Isolated rapid eye movement (REM) sleep behavior disorder (iRBD) is characterized by dream enactment behaviors and loss of physiological atonia during REM sleep. It is considered a prodromal stage of alpha-synucleinopathies and may result from dysfunction of brainstem structures regulating muscle tone in REM sleep. Whether other REM sleep features are simultaneously affected remains unclear. Here, we investigated alterations in REM sleep microstructure, including phasic REM sleep, sawtooth waves (STW) and non-REM/REM sleep transitions, in iRBD and RBD associated with Parkinson’s disease (PD+RBD). We retrospectively included 20 patients with iRBD (85% male, 66.5[63–68]years), 20 patients with PD+RBD (75% male, 62.5[57.5-65]years) and 20 controls (75% male, 67[61–70]years). REM sleep without atonia (RSWA), bursts of REMs and STW bursts were manually scored. Phasic REM sleep proportion (derived from REMs), STW density/duration/frequency and the duration of NREM/REM transitions were compared between groups with a general linear mixed-effects model. Phasic REM sleep proportion was higher in the iRBD group (26.5[21–33]%) than in control (16.4[12.5-22.3]%, p-corrected=0.005) and PD+RBD (17.6[13.9-21.7]%, p-corrected=0.005) ones. Non-REM/REM transitions showed a duration gradient, increasing from controls (119.0[58.5-186.1]sec) to iRBD (212.1[68.5-391.4]sec, p-corrected=0.0038) and PD+RBD (375.8[217.6-514.6]sec, p-corrected<0.001) patients. STW density and duration were reduced in the PD+RBD group only (1.33[1.1-1.54]/min; 2.13[1.70-2.69]sec) vs controls (1.74[1.52-2.05]/min, p-corrected=0.005; 2.98[2.18-4.11], p-corrected<0.001), whereas altered STW spectral content was observed in both patient’s groups with a power shift toward higher frequencies (both p<0.001 vs controls). These results reinforce the hypothesis that REM sleep dysregulation in RBD extends to REM-specific electrophysiological features beyond loss of muscle atonia and dream enactments.
Statement of Significance
This study compared rapid eye movement (REM) sleep microstructure between patients with isolated REM sleep behavior disorder (iRBD) or RBD associated with Parkinson’s disease (PD+RBD), and controls. We found some altered REM sleep features in patient groups versus controls, as increased phasic REM sleep proportion in iRBD and reduced sawtooth waves (STW) density and duration in PD+RBD. Both groups exhibited altered STW spectral characteristics with a shift toward higher frequencies. Additionally, we observed a gradient in the duration of NREM/REM sleep transitions, increasing from controls to patients with iRBD and peaking in patients with PD+RBD, who exhibited the longest transitions. These findings highlight that REM sleep anomalies in RBD extends beyond atonia loss and dream enactments, encompassing broader microstructural changes.
