Phenotypic Shift during Treatment of Plaque Psoriasis with Ixekizumab.

We present a case of a patient with longstanding psoriasis vulgaris who developed an atopic dermatitis-like eruption following long-term IL-17A inhibitor therapy. Following many years of excellent disease control with secukinumab and later ixekizumab, he developed a de novo eczematous eruption, which showed spongiotic dermatitis upon biopsy. The patient was successfully treated for both psoriasis and atopic dermatitis with upadacitinib, a Janus kinase inhibitor. This case suggests an interplay between Th1/Th17 and IL-4/IL-13 immune axes during prolonged biologic therapy, potentially due to upregulation of IL-4 following IL-17 blockade. It highlights the complex immune interactions in inflammatory skin diseases and demonstrates the utility of broader cytokine inhibition in managing evolving presentations.