Minimal clinically important change in patients with cervical dystonia: Results from the CD PROBE study

OBJECTIVE: To determine the minimal clinically important change (MCIC) on Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) scores using data from Cervical Dystonia Patient Registry for Observation of OnabotulinumtoxinA Efficacy (CD PROBE), which captured real-world practices and outcomes.

METHODS: Changes in the baseline TWSTRS scores (point and percentage changes) were compared to changes in the Patient and Clinician Global Impression of Change (PGIC and CGIC) ratings. Using logistic regression, the discrimination of the model was determined.

RESULTS: Among the 479 patients who completed all TWSTRS assessments, the mean TWSTRS Total score significantly decreased from baseline (39.2) to the final visit (27.1) (P < .0001). TWSTRS Total score point changes that compared with PGIC assessments "very much improved," "much improved" or better, and "minimally improved" or better were -11, -9, and -8, respectively, and were similar to previously published changes (ie, a decrease of ≥10 points). TWSTRS Total score data met indicators of good cutoffs for discrimination of the model including ≥70% percentage of outcomes correctly classified when compared with PGIC ratings. The TWSTRS Total score mapped to PGIC and CGIC ratings better than any TWSTRS subscale score.

CONCLUSIONS: The MCIC for improvement was ≥8 points based on mean TWSTRS Total scores in patients with cervical dystonia when compared against the patient-based evaluation of benefit (PGIC).