PD15 Predicting psoriasis response to ultraviolet B phototherapy: how much do missed appointments and early treatment response impact outcome?

Abstract

Narrowband ultraviolet B (NB-UVB) phototherapy is an established treatment for psoriasis; however, real-world treatment courses are frequently interrupted by missed sessions. Evidence defining whether imperfect adherence affects outcomes, and whether early treatment response is associated with outcome, remains limited in routine practice. We conducted a retrospective observational cohort study of adults (> 16 years) undergoing NB-UVB phototherapy between March and October 2024. Patients were included if baseline, midtreatment and end-of-treatment Psoriasis Area and Severity Index (PASI) scores were recorded with attendance data. The minimum accepted treatment completion was a 16-session course. Treatment adherence was calculated as the proportion of attended sessions relative to those scheduled. The outcome was the percentage PASI reduction from baseline. Overall, 122 patients were included (74 male, 48 female), with a median age of 48 years (range 19–82) and a median baseline PASI of 10.4 (range 3.2–32.1). The median number of treatments attended was 24 (range 20–30). Patients missed a median of 2 sessions (range 1–16). Patients demonstrated substantial improvement, with a median 82% PASI reduction. PASI improvement was similar across adherence levels within the cohort, with linear regression demonstrating no significant association between adherence and PASI improvement (R2 = 0.005, P = 0.46). A nonsignificant trend of poorer outcomes with lower attendance was observed, but numbers with more than three missed treatments were low. Early treatment response was significantly associated with outcome. Patients achieving a ≥ 30% week 3 PASI reduction had greater final PASI improvement (median 86%, interquartile range 75–92) than those without an early response (median 75%, interquartile range 57–84; P = 0.004), which is consistent with previous findings. Overall high adherence limited assessment of psoriasis clearance with lower attendance levels, but occasional missed treatments were not associated with poorer outcome. Week 3 PASI response may help to guide continuation decisions and support pragmatic service delivery.