Clinical case series: Emergence of psoriatic arthritis during biologic IL-23 pathway inhibition therapy for psoriasis.

Psoriasis (PsO) and psoriatic arthritis (PsA) are increasingly recognized as manifestations within the spectrum of psoriatic disease, and emerging observational data suggest that biologic therapy targeting interleukin-23 (IL-23) may reduce the risk of incident PsA. This finding remains controversial given the potential for channeling and information bias. Here, we describe five patients with long-standing PsO who developed new-onset PsA while achieving excellent skin clearance with IL-23 or IL-12/23 inhibitor therapy (risankizumab in four patients and ustekinumab in one). The time from the initiation of IL-23 pathway inhibition to PsA diagnosis ranged from 5 to 63 months. All patients met the ClASsification criteria for Psoriatic ARthritis, with musculoskeletal manifestations including dactylitis, synovitis, tenosynovitis, and enthesitis, and two patients had erosive changes on imaging. Joint symptoms improved in the majority of patients after transition to an IL-17-targeted biologic. These cases indicate that IL-23 pathway inhibition may not reliably prevent the onset of PsA and may contribute to its development in susceptible individuals. Thus, this series underscores the importance of ongoing musculoskeletal surveillance in patients with PsO receiving IL-23-targeted therapy, even when skin disease is completely controlled.