Rest‐Activity Pattern Alterations in Idiopathic REM Sleep Behavior Disorder

Objective The purpose of this study was to investigate the differences in actigraphy‐measured rest‐activity patterns (eg, sleep–wake cycle, circadian rest‐activity rhythm, and physical activity) across different stages of α‐synucleinopathy. Methods We compared alterations in 7‐day actigraphy‐measured rest‐activity patterns among patients with clinically diagnosed α‐synucleinopathies (n = 44), and their age‐, sex‐, and body mass index (BMI)‐matched patients with idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD, n = 88), and non‐rapid eye movement (REM) sleep behavior disorder (RBD) controls (n = 44) in a case–control study (study 1) and between convertors (n = 22) and their age‐, sex‐, BMI‐, iRBD‐duration, and follow‐up duration‐matched non‐convertors (n = 66) in a prospective nested case–control study (study 2). Results In study 1, there were significant increases (all p values were adjusted by false discovery rate < 0.01) in probable napping behaviors (percentage, duration, and episodes), activity fragmentation (estimated by k AR ), and physical inactivity during active periods across controls, and iRBD, to clinically diagnosed α‐synucleinopathies. In study 2, higher levels (all p values were adjusted by false discovery rate < 0.05) of baseline objective probable napping, activity fragmentation, and physical inactivity during active periods were associated with the conversion of patients with iRBD into clinically diagnosed α‐synucleinopathies at 2 years of follow‐up with medium to large effect sizes (Cohen's d: 0.56 to 0.80). These findings were further supported by functional linear modeling analyses. Interpretation Rest‐activity pattern alterations, mainly objective probable napping behaviors, activity fragmentation, and physical inactivity during active period, emerge as early as at the stage of iRBD, which serves as early and robust prodromal markers of the conversion of iRBD into clinically diagnosed α‐synucleinopathies. ANN NEUROL 2020;88:817–829