Objective: To determine whether digitized spiral analysis captures severity of dystonia in comparison to motor scores from the clinical gold standard, the Burke-Fahn-Marsden rating scale (BFM).

Background: Measures for detection and quantification of dystonia are needed to more carefully measure progression of disease and response to therapy. Assessments of drawing and writing facilitate objective evaluation of brachial dystonia. Digitized spiral analysis is a non-invasive test that captures kinematic, dynamic, and spatial attributes of freely drawn Archimedes spirals, and computes a series of spiral indices to quantify motor performance. In addition to an overall rating score, the BFM allows quantification of individual limb scores.

Methods: 23 dystonia patients (mean age: 31.6yrs; 8-66) with mutations in TOR1A (DYT1; n=12) or THAP1 (DYT6; n=11) drew 10 spirals with each hand on a digitizing tablet. BFM motor scores were assessed at the time of examination or based on video review. Spirals from the more dystonic arm (14 dominant, 9 non-dominant) were analyzed (mean arm BFM: 6.1; 1-16).

Results: A measure of spiral irregularity (0.67; p<0.001) most strongly correlated with the affected arm motor score on the BFM. Overall spiral severity (0.56; p=0.006), mean drawing speed (-0.49; p=0.02), mean downward pressure (0.47; p=0.02), and the residual of radius versus theta (0.51; p=0.01) also correlated.

Conclusions: Spiral indices derived from digitized drawing and analysis correlate with a standard clinical rating score for dystonia severity. Spiral analysis may be more sensitive than clinical rating scores, as the BFM is based on clinician rating only and is not tailored specifically to brachial dystonia. Subtle differences in brachial dystonia may not be captured by BFM. Assessment of improvement of brachial dystonia following therapeutic intervention, such as deep brain stimulation, may lend insight into determining the sensitivity of spiral analysis to changes in symptom severity.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/digitally-captured-archimedes-spiral-indices-correlate-with-clinical-assessment-of-dystonia-severity/