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Case Reports

Abstract

Dupilumab, a monoclonal antibody targeting IL-4 and IL-13 and the first biologic therapy approved by FDA for atopic dermatitis, may very rarely be associated with mycosis fungoides (MF). Various studies have implicated it in the unmasking, progression or rarely improvement of MF. A few studies have also shown its association with a benign reversible lymphoid reaction mimicking MF, although these lymphoid reactions mostly show CD30 overexpression. We report a case in a 64-year-old male with history of chronic hepatitis C, who presented with erythematous patches and plaques involving the trunk and extremities. A left lateral upper back biopsy demonstrated spongiotic dermatitis, consistent with atopic dermatitis. He was initiated on dupilumab (Dupixent) and in 3 months developed progressive diffuse erythrodermic rash with flaking and severe pruritus. The patient was then empirically started on oral cyclosporine, and a left upper arm biopsy was obtained. Sections of the biopsy demonstrated dense superficial dermal lymphocytic infiltrate with prominent epidermotropism, composed of small to mildly enlarged cells and hyperchromatic irregular nuclei. There was associated psoriasiform spongiotic epidermis with abundant eosinophils in the dermis and eosinophilic exocytosis/eosinophilic spongiosis. Immunohistochemical stains revealed a predominance of CD3-positive T-cells in the infiltrate with CD4:CD8 ratio of >10:1. CD30 immunostaining was negative and CD5 and CD7 were preserved. T-cell receptor gene rearrangement studies by PCR demonstrated small peaks. Overall findings were consistent with mycosis fungoides.  The patient has remained off Dupixent as well as cyclosporine for 3 months and has shown improvement in his rash.