Refractory Psoriatic Lesions in Japanese Patients Before and After Switching Biologics

Biologics can improve disease control in patients with psoriasis vulgaris (PsO) and psoriatic arthritis (PsA); however, refractory regions may persist despite biologic therapy. This study aimed to evaluate refractory anatomical regions in patients with PsO and PsA who underwent biologic switching. We retrospectively analyzed 71 biologic-switching episodes from 50 patients treated at Jichi Medical University Hospital between January 1, 2010 and December 31, 2019. Patients who underwent more than one biologic switch contributed multiple switching episodes. Refractory regions were assessed across 13 anatomical regions at the time of biological switching and at the end of the observation period. The lower extremities were the most frequently affected refractory region in both PsO and PsA, followed by the upper extremities in PsO and the scalp in PsA. Overall, the distribution of refractory regions was broadly similar before and after biologic switching. Improvement was defined as complete disappearance of a lesion that had been explicitly documented as present before biologic switching. Regions explicitly documented as lesion-free before switching were classified as non-improved, whereas regions without documentation regarding the presence or absence of a lesion before switching were excluded from the analysis. A logistic generalized linear mixed-effects model with a random intercept for switching episode was used to account for within-episode correlation among anatomical regions. The oral-to-biologic group had higher odds of documented lesion improvement than the biologic-to-biologic group (odds ratio, 2.12; p < 0.001), whereas disease subtype was not significantly associated with documented lesion improvement (PsO vs. PsA: odds ratio, 1.03; p = 0.876). These findings suggest that patients requiring biologic-to-biologic switching may represent a more treatment-refractory population. The lower extremities remained a particularly challenging anatomical region after biologic switching. Further prospective studies are warranted to clarify the factors associated with site-specific treatment response.