PD20 The impact of circadian rhythm on phototherapy treatment in psoriasis

Abstract

Psoriasis exhibits circadian rhythmicity, and chronotherapeutic benefits have been described for topical treatments. Circadian disruption, seen in shift work or time zone travel, may influence inflammatory pathways and treatment outcomes; however, the impact of circadian factors on phototherapy response remains largely unexplored. We postulated that alignment between chronotype and treatment timing, recent time zone travel and night-shift work might influence clinical response to ultraviolet B (UVB) phototherapy in psoriasis. We analysed 174 patients with psoriasis treated with UVB phototherapy between January and December 2025. Psoriasis Area and Severity Index (PASI) and Dermatology Life Quality Index (DLQI) were recorded at baseline and end of treatment. Circadian-related variables were collected using questionnaires, including self-rated chronotype (morning, evening or intermediate), treatment time, recent time zone travel and night-shift work. Chronotype alignment was defined as concordance between chronotype and treatment timing (morning types treated early, evening types treated later). Patients had moderate baseline disease (median PASI 12.6). Most completed ≥ 24 UVB sessions (n = 116). Night-shift (n = 19) and non-night-shift workers (n = 155) had identical baseline median PASI (12.6). Night-shift workers showed greater numerical PASI reductions (−14.6 vs. −9.6), while DLQI (median 12) improvements were similar (−8.6 vs. −8.7). Rates of PASI 50 (≥ 50% improvement from baseline) (92.3% vs. 86.4%) and PASI 75 (69.2% vs. 54.9%) were high in both groups. Treatment timing (early: 07.00 h to 09.59 h, n = 73; late morning: 10.00 h to 11.59 h, n = 48; early afternoon: 12.00 h to 14.40 h, n = 53) did not meaningfully influence response. PASI and DLQI improvements were similar in chronotype-aligned (n = 96) and misaligned patients (n = 78) (PASI reduction −9.7 vs. −10.9; DLQI −8.5 in both), with comparable PASI 50 and PASI 75 rates. Patients with recent time zone travel (n = 53) had similar PASI improvement to nontravellers (n = 121) (−10.3 vs. −10.2). Phototherapy response was not significantly influenced by chronotype alignment, treatment timing or time zone travel. Although night-shift workers showed greater PASI improvement, small subgroup sizes and missing data limit interpretation. These findings suggest circadian factors may not impact short-term phototherapy response, but further prospective studies are warranted.