PSS20 Mediation Modeling and Measurement Characteristics of the Itch Severity Score from a Phase 2B Trial of Oral CP-690-550 in Patients with Moderate-to-Severe Plaque Psoriasis

In a 12-week, double-blind, placebo-controlled Phase 2b trial involving 197 patients with moderate-to-severe plaque psoriasis, the oral Janus kinase inhibitor CP-690,550 significantly reduced pruritus, with direct effects on the Itch Severity Score (ISS) ranging from 70%-81% compared to placebo (p<0.001). The ISS showed acceptable test-retest reliability (intraclass correlation: 0.83) and correlated well with other measures, suggesting CP-690,550 had a direct, beneficial effect on pruritus. Additionally, a review of instruments for measuring hair growth and alopecia identified four potential tools, though none met the US FDA's PRO Guidance requirements. The Hair Growth Questionnaire could be revised for women, and the Hair Problem List or WAA-QOL could be adapted for broader relevance.