Objective: To evaluate the relative contributions of cognitive and motor factors to handwriting performance in patients with MSA and PD using quantitative tablet-based tasks.

Background: Micrographia, defined as a pathological reduction in handwriting size, is frequently observed in PD and also occurs in MSA. Despite longstanding recognition, the pathophysiological mechanisms underlying micrographia remain incompletely understood, and comparative data between MSA and PD are limited.

Method: We enrolled 11 patients with MSA, 53 with PD, and 52 age-matched healthy controls. Participants performed handwriting tasks on a high-resolution tablet. They were instructed to write the Japanese character “あ” ten times consecutively along a horizontal line, matching the size of a displayed reference sample. Handwriting kinematics, including character size, pen pressure, and writing speed, were analyzed. Time-series data were exported as CSV files and processed using a custom MATLAB program. For each character, writing size was quantified as the area of the bounding rectangle and expressed as a ratio relative to the reference sample. In the free-writing task, participants who consistently produced characters smaller than the reference (p < 0.05; one-sample t-test) were classified as consistent micrographers. Those showing a significant progressive decrease in character size over successive trials (p < 0.05; linear regression with writing order as the predictor) were classified as progressive micrographers. Group differences among MSA, PD, and controls were assessed using t-tests.

Results: Both MSA and PD patients exhibited significantly smaller, slower, and lower-pressure handwriting compared with controls. Among micrographers, consistent micrographia was observed in 27% of MSA patients and 47% of PD patients, whereas progressive micrographia was observed in 18% of MSA patients and 9% of PD patients. No significant differences were found between MSA and PD in character size, trajectory length per character, or writing time per character.

Conclusion: Micrographia was observed in both MSA and PD at comparable frequencies, with both consistent and progressive subtypes present in each disorder. Quantitative handwriting measures did not significantly differ between the groups.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/micrographia-in-parkinsons-disease-and-multiple-system-atrophy-a-quantitative-tablet-based-handwriting-study/