Minimal clinically important change in the Toronto Western Spasmodic Torticollis Rating Scale

Abstract

Objectives: To characterize the minimal clinically important change (MCIC) after treatment in cervical dystonia patients using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS).

Methods: Changes in the TWSTRS from an observational study of abobotulinumtoxinA in the routine management of cervical dystonia (NCT01314365) were analyzed using the Patient Global Impression of Change (PGIC) as anchor.

Results: For the overall population (N = 304, baseline TWSTRS-Total score 43.4 ± 19.4), the MCIC for the TWSTRS Total score was -11.9 (95%CI: -13.9, -10.0; p < 0.0001). However, thresholds ranged from -3.2 to -18.0 dependent on baseline severity. TWSTRS-Total scores improved linearly by 3 points for every one-point PGIC increase. There was similar linearity between the graded PGIC categories and TWSTRS subscale scores (severity, disability, and pain).

Conclusions: A 3-point change is the minimal clinically important change after treatment using TWSTRS as endpoint with higher cutoffs for greater baseline disease severity. For an average trial population (TWSTRS-total: 40-45), a 12-point decrease is clinically meaningful.

Keywords: Botulinum toxin; Cervical dystonia; Minimal clinically important change; Toronto western spasmodic torticollis rating scale; abobotulinumtoxinA.