INTRODUCTION: Plaque psoriasis 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 psoriasis.
METHODS: Pooled, blinded, 16-week data from 1002 patients in the BE VIVID and 
BE READY bimekizumab phase 3 trials were analysed. The suitability of the P-SIM 
missing score rule (weekly scores considered missing if ≥ 4 daily scores were 
missing) was assessed. 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 predefined using PASI/IGA scores. Sensitivity to change over 16 weeks 
was evaluated; responder definition (RD) thresholds were explored.
RESULTS: The missing score rule used did not impact P-SIM scores. 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 "skin 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 known groups at 
week 16, confirming known-groups validity. Changes from baseline to week 16 in 
P-SIM and other clinically relevant outcomes were strongly correlated (> 0.5; 
weaker with ClinROs), establishing sensitivity to change. Anchor-based RD 
analyses determined a four-point P-SIM item score decrease as indicative of 
marked clinically meaningful improvement.
CONCLUSION: P-SIM scores demonstrated good reliability, validity and sensitivity 
to change. A four-point RD threshold could be used to assess 16-week treatment 
effects.
TRIAL REGISTRATION: BE VIVID: NCT03370133; BE READY: NCT03410992.