Abstract
To the Editor:
Mycosis fungoides (MF), the most common cutaneous T-cell lymphoma, can mimic clinically and histopathologically diverse common and rare inflammatory skin conditions in its early stage. 1 We report a case in which dupilumab therapy for presumed atopic dermatitis (AD) unmasked underlying MF.
A 72-year-old man presented with a 20-year history of pruritic skin eruptions. Examination showed infiltrative facial erythema (Fig. 1A). A biopsy in 2018 was consistent with eczematous dermatitis (Fig. 1B). In June 2023, he was diagnosed with AD and started on dupilumab (300 mg biweekly). While most symptoms improved, his facial lesions worsened paradoxically despite topical triamcinolone acetonide-econazole and tacrolimus ointment.
A repeat facial biopsy revealed a dense dermal lymphocytic infiltrate (Fig. 1C). Immunohistochemistry showed CD4+ predominance (Fig. 1D), which, in the clinical context, raised suspicion for MF. Subsequent interferon α-2a therapy achieved significant facial lesion resolution. (Fig. 1E).
This case highlights a critical diagnostic challenge. Dupilumab is highly effective for moderate-to-severe AD, 2 but its use has been associated with “dupilumab facial redness” and the unmasking or progression of subclinical MF. 3 The inhibition of the IL-4/IL-13 pathway may disrupt the local immunological equilibrium, allowing latent malignant T-cell clones to proliferate. 4
Our experience underscores that MF must be considered in the differential diagnosis of adult-onset, refractory eczematous dermatitis, especially when facial lesions persist or worsen paradoxically during biological therapy. As recommended by recent reviews, 5 histopathologic reassessment is strongly recommended before initiating biologics in atypical cases and when new or progressive lesions arise during treatment. Early recognition of MF significantly alters management and improves prognosis.