Handwriting Movement Abnormalities in Symptomatic and Premanifest Huntington's Disease

Background Kinematic measures of handwriting movements are sensitive to mild subclinical motor abnormalities stemming from a wide range of disorders involving the basal ganglia including Huntington's disease (HD). Prior research has not investigated handwriting movements in at-risk individuals in the premanifest stage of HD. Objectives The purpose of this study was to examine whether handwriting movement abnormalities are present prior to clinically manifest chorea in HD. Methods A total of 38 symptomatic HD, 30 gene-positive premanifest, and 25 healthy control participants completed handwriting tasks consisting of circles, loops, sentences, and spirals with a noninking pen on a digitizing tablet. Multiple measures of pen stroke kinematics and pressure were measured along with the cognitive and motor status of each participant. Burden of pathology and CAG x age product scores were obtained from each participant with HD. Results Participants with HD exhibited significantly longer and more variable stroke durations, decreased handwriting smoothness, and increased and more variable pen pressures when compared with the healthy controls. We found significant positive associations between stroke duration and both burden of pathology and CAG x age product. Results from a discriminant function analysis revealed a 7-factor model that distinguished premanifest from healthy controls with 85% accuracy. Factors in the model included greater variability in stroke amplitude, velocity and pen pressure, higher levels of pen pressure, longer stroke durations, and lower velocities for combinations of handwritten circles, sentences, and spirals. Conclusions These findings support the clinical utility of dynamic measures of handwriting kinematics as a potential early behavioral biomarker in HD.