Dissociable Handwriting Domains in Parkinson's Disease?

BACKGROUND: Handwriting abnormalities in Parkinson's disease (PD) extend beyond classical micrographia and may involve multiple graphomotor domains with distinct clinical and mechanistic correlates. OBJECTIVES: To investigate whether distinct handwriting domains demonstrate dissociable relationships with differential diagnostic performance, cognitive function, motor severity, and dopaminergic responsiveness. METHODS: We evaluated tablet-based handwriting kinematics in 60 PD and 58 essential tremor (ET) patients using a standardized sequential writing task performed on a digital tablet. Spatial, temporal, pressure-related, and decrement measures were analyzed together with cognitive performance, levodopa responsiveness, and multivariate clinical associations. RESULTS: Compared with ET, PD patients demonstrated significantly smaller final-segment handwriting area (991 ± 582 vs. 1623 ± 710, p < 0.001, d = 0.97), lower mean pressure (0.69 ± 0.17 vs. 0.81 ± 0.13, p < 0.001, d = 0.80), and higher prevalence of progressive reduction ≥10% (58.3% vs. 10.3%, OR = 12.13). Area ratio showed the strongest univariate discriminative performance (AUC = 0.814), whereas multivariate regression identified final-segment area (β = -0.52, p < 0.001) and mean pressure (β = -0.31, p = 0.003), but not decrement measures, as independent predictors of PD. Within the PD group, smaller final-segment handwriting area independently correlated with greater motor severity (β = -0.39, p = 0.004) and poorer visuospatial performance (β = +0.27, p = 0.028), whereas pressure-related measures demonstrated greater levodopa responsiveness. In contrast, decrement measures showed comparatively weak independent associations with motor severity, cognition, and dopaminergic responsiveness. CONCLUSIONS: Handwriting abnormalities in PD appear multidimensional and demonstrate partially dissociable relationships with motor severity, visuospatial performance, levodopa responsiveness, and differential diagnostic performance. These findings suggest that different handwriting domains may reflect complementary aspects of graphomotor dysfunction rather than a unitary phenomenon.