Nocturnal eye movements in patients with idiopathic rapid eye movement sleep behaviour disorder and patients with Parkinson's disease

Objectives/Introduction:Patients with idiopathic rapid eye move-ment (REM) sleep behaviour disorder (iRBD) have a high risk of con-verting into α‐synucleinopathies due to an early neurodegenerative process involving lower brain stem areas. Eye movements (EMs) are controlled by neurons located in the lower brain stem, midbrain, and frontal areas, and are therefore vulnerable to be affected by an early neurodegeneration. Several studies have reported impairment of the oculomotor function in patients with Parkinson's disease (PD) during wakefulness, but no studies have investigated how neurodegeneration affects EMs during sleep. We aimed to evaluate nocturnal EMsin iRBD and PD hypothesizing that these patients present abnormalEMs during sleep.Methods:A total of 28 patients with periodic leg movement disor-der (PLMD; 15 males; 60.3 ± 11.9 years), 24 with iRBD (17 males;63.0 ± 10.1 years), 23 with PD without RBD (PD‐RBD; 14 males;61.4 ± 5.4 years), 29 with PD and RBD (PD+RBD; 19 males;63.3 ± 5.1 years), and 24 controls (11 males; 56.7 ± 9.9 years) were included. A previous validated EM detector was used to automatically detect periods with any kind of EMs in artefact‐free epochs between lights off and on. The EM coverage was computed as the percentage of time containing EMs, during stages of wakefulness,N1, N2, N3, and REM sleep. Between‐group comparisons were performed using Wilcoxon‐Ranksum tests, and the Benjamini‐Hoch-berg procedure with a false discovery rate of 0.1 was used to con-trol for multiple testing.Results:We found that PD+RBD had significant less EM coverage during wakefulness compared to controls (p<0.001), and signifi-cantly higher EM coverage during N2 compared to controls(p= 0.003) and PLMD (p= 0.004). Furthermore, PD‐RBD showed significantly higher EM coverage during N2 compared to controls(p<0.001) and PLMD (p= 0.001). Same trends were observed between iRBD and controls in wakefulness and N2, but were not significant after correction for multip