Paradoxical reaction of pustular psoriasis after switching to risankizumab

Biologics are advanced treatments for psoriasis that target specific immune pathways.Risankizumab, a humanized IgG1 monoclonal antibody against the p19 subunit of interleukin-23(IL)-23, is approved for moderate-to-severe plaque psoriasis.A 26-year-old man with a 12-year history of plaque psoriasis had received adalimumab 40 mg every other week for five years.Because adalimumab did not achieve PASI 75, the patient was switched to risankizumab 150 mg.Approximately seven days after the first treatment, he experienced a paradoxical reaction presenting as pustular psoriasis on the lower extremities.Considering the rapid onset after risankizumab treatment and the absence of prior pustular disease, we diagnosed paradoxical pustular psoriasis attributable to risankizumab.The episode was controlled with systemic corticosteroids.After discontinuing risankizumab, secukinumab 300 mg led to rapid improvement, with no recurrence over 18 months.We report a case of paradoxical reaction to risankizumab, with a morphological change from plaque to pustular lesions.