Atypical Dermatophytosis in Patients Treated by JAK Inhibitors

Janus kinase (JAK) inhibitors are commonly used to treat immune-mediated diseases by modulating the JAK-STAT signalling pathway. While these agents are therapeutically effective, they may also impair immunity, including antifungal response. Here, we present five cases of atypical dermatophyte infections in patients treated with baricitinib or upadacitinib. Their clinical presentations and treatment regimens were summarised to highlight the atypical features and the presumed effects of JAK inhibitors. Patients presented with erythematous indurated plaques, clustered firm papules, and widespread thin plaques with scaling and erosions. PCR and fungal cultures confirmed infections with Trichophyton tonsurans, Trichophyton rubrum, Trichophyton verrucosum, and Microsporum canis. Treatment with systemic antifungal agents such as terbinafine, itraconazole, and griseofulvin was effective. In some cases, the dosage of JAK inhibitors was reduced during antifungal therapy. Clinicians should be vigilant for cutaneous fungal infections in JAK inhibitor-treated patients with new rashes. The immunomodulatory effect of JAK inhibitors may attenuate the clinical manifestation and lead to delayed recognition of dermatophytosis.