OBJECTIVES : Plaque psoriasis (PSO) can significantly impact patients’ quality of life. We assessed psychometric properties of the Psoriasis Symptoms and Impacts Measure (P-SIM), developed to capture patients’ experiences of signs, symptoms, and impacts of PSO.

METHODS : Pooled, blinded data from 1,002 patients in the BE VIVID (NCT03370133) and BE READY (NCT03410992) bimekizumab phase 3 trials were analysed. Average weekly scores (considered missing if >3 daily scores were missing) were derived for the 14 P-SIM items.

Test-retest reliability was evaluated using intraclass correlation coefficients (ICCs). Convergent validity was assessed between P-SIM and relevant patient-reported outcome (PRO) (Dermatology Life Quality Index [DLQI], DLQI Item 1 [skin symptoms], Patient Global Assessment of Psoriasis) and clinician-reported outcome (ClinRO) scores (Psoriasis Area and Severity Index [PASI], Investigator’s Global Assessment [IGA]) at baseline and Week 16. Known-groups validity was assessed, comparing P-SIM scores between patient subgroups pre-defined using PRO/ClinRO measures. 16-week responsiveness was evaluated; responder definition (RD) thresholds were proposed.

RESULTS : 16-week average P-SIM completion rate was 85.2%. Test-retest reliability analyses demonstrated excellent score reproducibility (ICC: 0.91–0.98). Inter-item correlations at baseline and Week 16 were strong (>0.5), apart from “Choice of clothing” with “Pain” and “Burning” at baseline (both 0.49). All P-SIM scores were moderately-to-strongly correlated with other outcomes, demonstrating convergent validity, apart from ClinROs (PASI, IGA) at baseline that had low variability. P-SIM scores discriminated between pre-defined subgroups at Week 16, confirming known‑groups validity. 16-week changes from baseline in P-SIM and other outcome scores were moderately-to-strongly correlated (>0.5; weaker with PASI, IGA), establishing responsiveness. Anchor-based RD analyses determined a 4-point P-SIM item score decrease as indicative of marked clinically meaningful improvement; lower thresholds (1.98–2.86; “Itch”, “Pain”, “Scaling” scores) were previously determined in phase 2b data analyses.

CONCLUSIONS : P-SIM scores demonstrated good reliability, validity, and responsiveness. A 4-point RD threshold could be used to assess 16-week treatment effects.