Wearable gyro sensors during forearm rotation (but not finger tapping) revealed greater upper-limb motor asymmetry in early, drug‑naïve PD versus SWEDD, with asymmetry indices correlating with clinical motor scores.

This study offers a quantitative, noninvasive sensor biomarker for distinguishing PD from SWEDD and for patient stratification in diagnosis and clinical trials, aiding translational work and trial enrollment though it does not advance mechanistic or therapeutic targets.

BACKGROUND: Bilateral motor asymmetry is a hallmark feature of Parkinson's disease (PD). However, few studies have quantitatively examined this feature in patients with scans without evidence of dopaminergic deficit (SWEDD). This study aimed to investigate upper limb asymmetry in bradykinesia among PD and SWEDD patients using gyro sensors, focusing on finger tapping and forearm rotation task. METHODS: We recruited 23 early-stage, drug-naïve PD patients, 23 SWEDD patients, and 20 age-matched healthy controls. We recorded gyro sensor signals during 15-s finger tapping and forearm rotation tasks. Bilateral asymmetry indices were calculated and compared among groups. In addition, repeated measure analysis of variance (ANOVA) was used to examine the interaction of task and group, and Spearman correlation analysis was conducted with clinical motor scores. RESULTS: No significant group differences were found during finger tapping. However, during forearm rotation, PD patients exhibited significantly greater asymmetry than SWEDD patients in several indices, including RMS angular velocity, peak angular displacement, peak power, and total power. Task × group interaction effects were significant only in forearm rotation, and asymmetry indices from forearm rotation showed significant correlations with clinical motor scores. CONCLUSIONS: Forearm rotation is a sensitive task for detecting motor asymmetry in PD and for differentiating PD from SWEDD. These results suggest that quantitative motor asymmetry indices using wearable sensors could aid clinicians in the identification of potential SWEDD.