Application of the Itch Severity Score in patients with moderate-to-severe plaque psoriasis: Clinically important difference and responder analyses.

The Itch Severity Score (ISS), a 0-10 numeric rating scale, was used to assess pruritus due to psoriasis in a Phase 2 b trial of tofacitinib, a novel oral Janus kinase inhibitor. 197 patients with moderate-to-severe plaque psoriasis were randomized to tofacitinib 2, 5 or 15 mg twice daily, or placebo. The ISS was recorded daily from baseline to week 2 and at study visits. Following good and recommended research practice, we performed analyses to examine the clinically important differences (CID) (between-group difference or within-group difference) and clinically important responders (CIR) (within-patient change) for the ISS. The CID and CIR were defined using Patient Global Assessment of psoriasis as an anchor and were estimated with a longitudinal model. A CID on the ISS was 1.64 and, by day 10, the mean changes from baseline in ISS values for the tofacitinib doses (placebo-adjusted) exceeded CID. A CIR on the ISS was a 30% improvement from baseline and, at week 12, 87.2% to 100% of patients receiving tofacitinib reached ≥30% improvement versus 29.4% of patients receiving placebo (p < 0.0001). Overall, the CID and CIR analyses play vital roles in the interpretation of the treatment effects measured by ISS.