Temporal progression of sleep electroencephalography features in isolated rapid eye movement sleep behaviour disorder.

Previous studies indicated that patients with isolated rapid eye movement (REM) sleep behaviour disorder (iRBD) exhibit alterations in spectral electroencephalographic (EEG), spindle, and slow-wave features. As it is currently unknown how these EEG features evolve over time, this study aimed to evaluate their temporal progression in patients with iRBD in comparison to controls. We included 23 patients with iRBD and 23 controls. Two polysomnographies (baseline and follow-up) were recorded with a mean (standard deviation) interval of 4.0 (2.5) years and were automatically analysed for sleep stages, spectral bandpower, spindles, and slow waves. We used linear models to evaluate differences at each time point, and linear mixed-effects models to analyse differences in temporal progression between the groups. At baseline, patients with iRBD presented EEG slowing both in REM (expressed as significantly reduced α-bandpower and increased δ-bandpower in frontal channels) and in non-REM (NREM) sleep (significantly increased slow-to-fast ratio in central channels). These differences vanished at follow-up. In both REM and NREM sleep, γ-bandpower was increased at follow-up in patients with iRBD, resulting in significantly different temporal progression between groups (in occipital channels during REM sleep and frontal channels during NREM sleep). Relative power of sleep spindles was significantly higher at baseline in patients with iRBD in frontal channels, but we observed a significant reduction over time in central channels. Finally, slow waves were significantly shorter in patients with iRBD at both time-points. Our results underscore the need of considering longitudinal data when analysing sleep EEG features in patients with iRBD. The observed temporal changes as markers of progression of neurodegeneration require further investigations.

A 24% prevalence of excessive fragmentary myoclonus in 500 consecutive sleep laboratory patients.

Excessive fragmentary myoclonus (EFM) is a frequent finding during routine video-polysomnography (VPSG). We aimed to automatically measure the prevalence of EFM according to current American Academy of Sleep Medicine (AASM) criteria, and the fragmentary myoclonus index (FMI) in sleep stage N1, N2, N3, rapid eye movement (REM) sleep and wake in a large patient population. A total of 500 VPSG recordings of patients admitted to the Sleep Laboratory, Department of Neurology, Medical University of Innsbruck, Austria, between May 1, 2022 and February 28, 2023, were included. EFM according to AASM criteria and FMI were computed by applying a previously validated algorithm. EFM was automatically detected in 121 of the 500 Sleep Laboratory patients (24.2%, 95% confidence interval 20.1%-28.9%). FMI increased with age, male gender, apnea-hypopnea-index (AHI), oxygen desaturation index (ODI), and periodic leg movements of sleep (PLMS) index. FMI was highest in REM sleep behaviour disorder (RBD), followed by neurodegenerative and internal medicine diseases, but the increase in the FMI was not explained by the disease itself but rather by the age and sex of the patients. Almost a quarter of our patient population had EFM. However, the prevalence of EFM does not allow the drawing of any conclusions about the pathophysiology of EFM or even the determination of a pathological FMI cut-off value. Associations of the FMI with age, sex, AHI, ODI and PLMS are in line with previous studies, but the FMI needs to be evaluated in different disease entities to learn more about its pathophysiology.