Deep profiling of nocturnal hypokinesia in multiple system atrophy and its clinical implications

Study objectives: Patients with multiple system atrophy (MSA) spend more time supine overnight. Assessing nocturnal hypokinesia (NH) in MSA via video polysomnography (VPSG) is limited in metrics and analysis depth. This study deconstructs NH by sleep-wake phases, develops new VPSG-based body transition parameters, and explores their utility in understanding NH's pathogenesis and therapeutic implications in MSA. Methods: We retrospectively reviewed VPSG data of 150 participants – 58 MSA, 42 obstructive sleep apnea (OSA), and 50 controls. We analyzed the proportion of sleep in each body position and corresponding apnea-hypopnea indices (AHIs). Additionally, we assessed sleep-wake phase-specific and composite body transition indices (BTIs) (intra-phase, sleep-to-wake, wake, and modified BTI). Body position statistics, BTIs, and supine-to-lateral AHI reduction were compared across the three groups. Results: The MSA group had a significantly higher rate of sleep-time-on-back (STOB) and a lower proportion of lateral sleep. They also showed a lower sleep-to-wake BT/BTI compared to control and OSA groups, with no differences in intra-phase and wake BT/BTI. Furthermore, both the MSA and OSA groups showed greater AHI reduction from lateral positioning compared to the control group, with no significant difference between the MSA and OSA groups. Conclusion: The proposed BTIs may serve as valuable adjuncts to sleep-time-on-back (%) in assessing NH, potentially indicating arousal-to-movement-arc impairment. Furthermore, NH-targeted treatments may benefit sleep-disordered breathing in patients with MSA.