Objective: To apply computerized spiral analysis to investigate upper limb kinematics and impact of deep brain stimulation (DBS) on motor dysfunction in Parkinson disease (PD) and essential tremor (ET).

Background: Computerized spiral analysis is a non-invasive test capturing kinematic dynamics and spatial featuresof Archimedean spirals. It computes a series of mathematical indices by to quantify motor performance and is validated with clinical rating scales in PD and ET. Clinical changes from DBS are typically evaluated subjectively, which lacks sensitivity for subtle changes. With the development of more sophisticated DBS targeting methods, we propose to document DBS outcomes to elucidate which spiral analysis indices reflect favorable outcomes and which do not.

Method: This retrospective study evaluated 99 subjects with PD (76), ET (13), or PD-ET (10) referred for DBS from 2002-2018 who underwent pre- and post-operative spiral analysis testing. Subjects freely drew 10 spirals with both hands on plain paper with an inking pen on a graphics tablet (Intuos4, Wacom Technology, Corp, Vancouver, WA). Acquisition and analysis software were written in Objective-C and MATLAB (The Mathworks, Natick, MA). We assessed a subset of indices with validated clinical correlates: overall degree of disease severity (DoS) corresponding to a 5-point (0-4) rating scale, second order smoothness (2ndSm) as a marker of bradykinesia, rigidity, and drawing irregularity, tightness as a correlate of micrographia, spiral width variation (SWVI) measuring ataxia, drawing speed from the start to end of each spiral, and tremor severity.

Results: DoS improved after DBS (p < 0.001), independent of target and correlated with motor UPDRS score improvement from 37 ± 15.8to 18.5 ± 9.9 (p<0.001). 2ndSm improved in all patients (p<0.001), independent of DBS target. The tremor severity decreased in both STN (p<0.001) and Vim (p<0.05) targets. SWVI only improved in Vim target in ET (p<0.05). DBS had no effect on tightness or drawing speed (p>0.05).

Conclusion: Spiral analysis provides objective and quantifiable correlates of clinical change after STN and Vim DBS. In this study, we show that spiral analysis discriminates those clinical features that improve after specific DBS targeting and clinical conditions from that do not change and suggest that these findings could be used to further refine DBS targeting and stimulation techniques.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spiral-analysis-evaluates-the-effects-of-deep-brain-stimulation-in-parkinson-disease-and-essential-tremor/