In patients with cervical dystonia who have an average Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) score of 40 to 45, an approximate 12-point decrease in the TWSTRS is considered clinically meaningful for demonstrating the efficacy of botulinum toxin treatment, according to study findings published in Parkinsonism and Related Disorders.
Investigators assessed changes in TWSTRS scores, which are used to assess cervical dystonia severity as well as treatment efficacy, in patients with cervical dystonia receiving abobotulinumtoxinA (n=304). The administration of treatment was performed over 5 treatment cycles, and the investigators assessed TWSTRS changes at baseline and 4 weeks following injection. In addition, the investigators examined Patient Global Impression of Change (PGIC) at 4 weeks with the 7-point Likert scale, with +3 as “very much improved” and −3 as “very much worse.”
At baseline, the TWSTRS total score was 43.4±19.4 in the modified intention to treat population. The majority of patients presented with complex cervical dystonia (67.2%).
For the PGIC categories of “very much improved” and “very much worse,” the TWSTRS-Total scores ranged from −19.63 to −5.89, respectively (P <.01). Each 1-point increase in the PGIC rating resulted in a 2.9-point improvement in the TWSTRS-Total scores, as demonstrated by the 2.9±0.51 least squares regression slope for the PGIC categories (P <.0001). According to the investigators, the minimal clinically important change (MCIC) in the TWSTRS in participants rated minimally improved (+1) on the PGIC at 4 weeks was −11.9 (95% CI, 13.9-10.0; P <.0001).
One limitation of this analysis was the lack of a control group, which could have assessed the differences between treatment with botulinum toxin and a control medication or placebo. In addition, the small sample sizes in some of the patient subcategories, including the worsening PGIC and “minimal improvement” categories, represent further study limitations.
The investigators suggest that the estimates found in this study may be “important for regulatory agencies, clinicians, and patients in properly assessing the clinical relevance of treatment responses” in abobotulinumtoxinA-treated patients with cervical dystonia.
Espay AJ, Trosch R, Suarez G, et al. Minimal clinically important change in the Toronto Western Spasmodic Torticollis Rating Scale [published online March 7, 2018]. Parkinsonism Relat Disord. doi:10.1016/j.parkreldis.2018.03.002