Validating an objective video-based dyskinesia severity score in Parkinson's disease patients.

Dyskinesia is a common side effect of prolonged dopaminergic therapy in Parkinson's disease patients. Assessing the severity of dyskinesia could help develop better pharmacological and surgical interventions. We have developed a semi-automatic video-based objective dyskinesia quantifying measure called the severity score (SVS) that was evaluated on 35 patient videos. We present a study to evaluate the utility of our severity score and compare its performance to clinical ratings of neurologists. In addition to the Unified Dyskinesia Rating Scale (UDysRS) score for each video, four neurologists provided three sets of time lapsed ratings and rankings of the 35 videos using a specifically developed protocol. The statistical analysis of our data using Kendall's tau-b and intra-class correlations shows that (a) ranking patient videos based on severity is suitable for studying the utility of the SVS, and (b) SVS exhibits moderate utility to quantify dyskinesia severity when compared to manual assessment of dyskinesia by neurologists using the UDysRS. These results support the effective use of SVS as an objective measure to quantify dyskinesia and the rationale for a ranking system that complements traditional rating scales.