Objective: Kinematic analysis of Archimedean spiral drawing in Writer’s cramp (WC) patients compared to healthy participants using a digitizing tablet.

Background: Spiral drawing using a digitizing tablet is a simple yet effective measure of handwriting kinematics. It is an accurate and non-invasive method for quantitative detection of hand-motor dysfunction in patients with movement disorders. It is already validated for tremor assessment in Parkinson’s disease and is gaining popularity for patients with hand dystonia. While spiral drawing is a part of routine clinical assessment in WC patients, pairing it with digitizing tablet could serve as a useful aid in objective clinical diagnosis, and as a sensitive method of measuring the effects of therapy on hand movements.

Methods: 15 WC patients, based on MDS consensus for the diagnosis of dystonia, and 14 age matched healthy volunteers were recruited. Writer’s Cramp Rating Scale was used for severity assessment in the patients. The participants were asked to perform the handwriting task on a Wacom® digitizing tablet, where they had to draw 9 spirals and trace 3 spiral templates. Average velocity, axial pen pressure, and normalized jerk (a measure of fluency) were the variables used for comparison. All participants were made to practice the task before the main recording. The test was recorded using the Pullman’s experiment on MovAlyzeR® software.

Results: The average velocity recorded for healthy controls was 4.151± 2.41 cm/s and 2.64± 1.39 cm/s for WC patients (p=0.054). The velocity difference between the first and the last trial was 1.45 ± SD cm/s for healthy, while 0.49 ± SD cm/s for WC (p=0.052) No significant difference in pen pressure was found (p= 0.215). The average jerk during tracing was 1136± SD cm/s3 for healthy and 3614.94± SD cm/s3 in WC patients (p= 0.018).

Conclusions: The result shows a strong statistical trend of lower writing velocity and higher normalised jerk in WC, while pen pressure remained comparable between the groups. The increased speed with trials in healthy controls suggests the influence of practice; but no such effect was present in WC patients. Interestingly, fluency worsened during tracing in the WC group. The data suggests that the above arrangement could be useful for early detection of motor abnormalities. Moreover, it could be used as an objective measure of subclinical effects of therapeutic interventions.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/handwriting-analysis-in-writers-cramp-using-a-digitizing-tablet/