An Empirical Comparison of Commonly Used Universal Rating Scales for Dystonia

Background: There are several widely used clinical rating scales for documenting the severity and distribution of various types of dystonia. Objectives: The goal of this study was to evaluate the performance of the most commonly used scales in a large group of adults with the most common types of isolated dystonia. Methods: Global Dystonia Rating Scale (GDRS) and the Burke-Fahn-Marsden Dystonia Rating Scale (BFM) scores were obtained for 3067 participants. Most had focal or segmental dystonia, with smaller numbers of multifocal or generalized dystonia. These scales were also compared for 209 adults with cervical dystonia that had Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) scores and 210 adults with blepharospasm that had Blepharospasm Severity Scale (BSRS) scores. Results: There were strong correlations between the GDRS and BFM total scores (r = 0.79) and moderate correlations for their sub scores (r > 0.5). Scores for both scales showed positive skew, with an overabundance of low scores. BFM sub-scores were not normally distributed, due to artifacts caused by the provoking factor. Relevant sub-scores of the GDRS and BFM also showed moderate correlations with the TWSTRS (r > 0.5) for cervical dystonia and the BSRS (r > 0.5) for blepharospasm. Conclusions: The BFM is more widely used than the GDRS, but these results suggest the GDRS may be preferable for focal and segmental dystonias. The overabundance of very low scores for both scales highlights challenges associated with discriminating very mild dystonia from other abnormal movements or variants of normal behavior.