Validation of a scoring algorithm for the clinician‐reported outcome tool ‘prurigo activity and severity (PAS)’ based on clinical studies of dupilumab in adults with prurigo Nodularis

Abstract Background Prurigo nodularis (PN) also known as chronic prurigo, is a chronic inflammatory skin disease characterized by intensely itchy nodules/lesions which occur due to intensive scratching. PN management is, in part, based on clinician evaluations of PN lesions, which can be supported by clinician‐reported outcomes (ClinRO) such as the Prurigo Activity and Severity (PAS) instrument. A 5‐item version of PAS was included in recent phase‐3 dupilumab PN trials (PRIME NCT04183335/PRIME2 NCT04202679). The PAS score was derived using the unweighted sum of 3‐items of the 5‐item PAS (range, 0–11; higher score indicates worse activity and severity): Item 2 (number of lesions), Item 5a (percentage of lesions with excoriations/crusts) and Item 5b (percentage of healed lesions) for use in clinical practice and for communication of treatment benefit to physicians. Objectives To evaluate the measurement properties of PAS score and derive within‐patient (responder definition) and between‐group improvement thresholds for interpreting changes in PAS score in patients with PN. Methods The data source was the pooled treatment group, intention‐to‐treat (ITT) data from the phase‐3 PRIME (NCT04183335) and PRIME2 (NCT04202679) studies evaluating the efficacy of dupilumab in adult patients with PN with ≥20 nodules and severe itch uncontrolled with topical therapies. PAS score reliability, validity and sensitivity to change were evaluated, and anchor‐ and distribution‐based methods were applied to derive meaningful change thresholds. Results The pooled ITT population included 311 patients (mean age 49.5 years, 65.3% female). Adequate to good psychometric properties were demonstrated for PAS score. The within‐patient meaningful improvement threshold was estimated as 3.0 points (absolute change) and 37% (per cent change). A 1.7‐point (absolute change) and 20% (per cent change) improvement were estimated to reflect a between‐group meaningful change in PAS score. Conclusions PAS score is a simple, clinically relevant indicator of PN lesion activity and severity supported by suitable psychometric performance.