Longitudinal progression of digital arm swing measures during free-living gait in early Parkinson's disease

Asymmetric arm swing reduction is a hallmark of early-stage Parkinson's disease (PD). We evaluated wrist sensor-based arm swing measures during free-living gait as digital progression biomarkers in 623 early-stage PD participants and 50 controls monitored continuously for one year (controls) or two years (PD). Biweekly measures were extracted from gait segments without other arm activities. Arm swing measures were reduced in PD, reduced on the most affected side, moderately correlated with clinical motor severity, and highly reliable. In unmedicated participants, most affected side measures declined over one year (standardized response means: −0.32 to −0.78) and two years (−0.51 to −1.10), exceeding an MDS-UPDRS Part III subscore at one year (−0.21) and matching it at two years (−0.83). In medicated participants, arm swing increased on the most affected side, which was associated with higher dopaminergic doses and dyskinesia. Overall, free-living arm swing measures are promising progression biomarkers in early, untreated PD.