Distinct handwriting kinematic profiles across Parkinson's disease subtypes

Handwriting impairment is common in Parkinson's disease (PD), but its relationships with clinical severity and motor phenotypes remain incompletely understood.

To characterize handwriting kinematics in PD and examine their associations with clinical severity and motor phenotypes.

Fifty-six patients with PD and 46 healthy controls (HC) performed a standardized digital handwriting task in the medication OFF state. Letter area, duration, pressure, writing speed, and the progressive micrographia (PM) index were analyzed. TD and AR subtypes were compared, and correlation and ROC analyses were performed.

PD patients showed significant handwriting abnormalities compared with HC. Using a >30% reduction in mean letter area to define categorical progressive micrographia, PM was observed in 8.9% of patients with PD and 2.2% of healthy controls (p = 0.219). The continuous PM index and twenty-letter duration showed discriminative performance, with AUCs of 0.753 and 0.718, respectively (both p < 0.001). Compared with TD patients, AR patients exhibited smaller writing areas (initial five-letter area, p = 0.042; twenty-letter area, p = 0.013; final five-letter area, p = 0.024) and slower writing speed (p = 0.012). Twenty-letter duration correlated with HY stage (r = 0.290, p = 0.030) and MDS-UPDRS-III scores (r = 0.404, p = 0.006). Overall, temporal parameters, particularly letter duration, were more closely associated with disease severity, whereas spatial measures showed weaker clinical correlations despite clear between-group differences.

Temporal measures were more closely associated with clinical severity, whereas spatial measures showed weaker and less consistent associations. Distinct handwriting kinematic profiles between TD and AR phenotypes suggest that quantitative handwriting analysis may provide complementary information on motor heterogeneity in PD.