Reliability, validity, and the ability to detect change of the Psoriasis Symptom Scale (PSS) in patients with plaque psoriasis.

The primary objective of the study was to evaluate the measurement properties of the patient-reported four-item Psoriasis Symptom Scale (PSS).: Analysis of phase-III data on the efficacy of risankizumab to assess psychometric characteristics of the PSS in patients with moderate-to-severe psoriasis. PSS items had a good range of symptom severity coverage. The PSS had good test-retest reliability (ICCs >0.90). Convergent and discriminant validity was indicated by moderate-to-strong correlations between the PSS and Dermatology Life Quality Index (DLQI), PSS pain item and EQ-5D pain/discomfort item at week 12 (0.63), and moderate negative correlation with EQ-Visual Analog Scale score at week 12 (-0.37). Known groups validity demonstrated as mean PSS total scores varied by Psoriasis Area and Severity Index (PASI) and Static Physician's Global Assessment (sPGA) defined groups ( < .0001). PSS total scores were responsive to changes in PASI score ( < .0001) and sPGA ( < .0001). PSS minimal, clinical, and meaningful change is estimated to be 1 to 2 points; a preliminary responder definition is a total change score of 3 to 4 points. The PSS is a short, valid unidimensional measure of psoriasis symptom severity, well suited for use in clinical trials.