Defining tic severity and tic impairment in Tourette Disorder

Treatment guidelines for Tourette's Disorder (TD) are based on patients' degree of tic severity and impairment. However, clear benchmarks for determining tic severity and impairment have not been established. This study examined benchmarks of tic severity and tic impairment using the Yale Global Tic Severity Scale (YGTSS) and the Clinical Global Impression of Severity (CGI-S).

Individuals with TD or another Tic Disorder (N = 519) recruited across nine sites were administered a diagnostic interview, the YGTSS, and the CGI-S. Correlations and trend analyses contrasted YGTSS scores across CGI-S ratings. A logistic regression model examined predictive benchmarks for tic severity, tic impairment, and global severity. Model classifications were compared against CGI-S ratings, and agreement was examined using kappa.

Spearman correlations between the CGI-S and YGTSS scores ranged from 0.54 to 0.63 (p < 0.001). Greater CGI-S ratings were associated with a linear stepwise increase in YGTSS Total Tic scores, Impairment scores, and Global Severity scores. Despite moderate-to-strong associations (ρ = 0.45-0.56, p < 0.001) between the CGI-S and predictive logistical regression models, only fair agreement was achieved when applying classification benchmarks (κ = 0.21-0.32, p < 0.001).

CGI-S ratings are useful to characterize benchmarks for tic severity, tic impairment, and global severity on the YGTSS. Logistic regression model benchmarks had only fair agreement with the CGI-S and underscore the heterogeneity of TD symptoms. Collectively, findings offer guidance on the delineation of tic severity categorizations to apply evidence-based treatment recommendations.