From Atopic Dermatitis to Pemphigus Herpetiformis: Navigating Overlapping Clinical and Histopathologic Features

Summary: A 24-year-old female, with a previous diagnosis of atopic dermatitis, presented with a 6-year history of a widespread pruritic rash refractory to topical and systemic corticosteroids, UVB phototherapy, and dupilumab. Examination revealed scattered pink papules, some edematous, coalescing into polycyclic plaques with overlying scale, without vesicles or mucosal involvement. Labs showed marked eosinophilia (4000/mm³). Skin biopsies demonstrated eosinophilic spongiosis with scattered apoptotic keratinocytes. Direct immunofluorescence revealed intercellular IgG/C3 staining with weak basement membrane staining. Indirect immunofluorescence showed cell surface IgG and IgA on primate esophagus. Anti-desmoglein 1 was elevated, anti-desmoglein 3 equivocal, anti-BP180 borderline elevated, and other serologies (ANA, ENA panel, anti-BP230, anti-laminin 332, anti-p200, anti-type VII collagen) were negative. PET scan and transvaginal ultrasound were unremarkable. Her presentation, histopathology, and serologic studies were most compatible with pemphigus herpetiformis. Treatment with prednisone, dapsone, and rituximab were initiated. This case highlights a challenging presentation with overlapping histopathologic and serologic findings, emphasizing the importance of a thorough evaluation to differentiate eczematous dermatitis from immunobullous diseases and drug-induced reactions. The patient’s eczematous eruption evolved over 6 years of treatment with dupilumab. It is unclear whether there was an initial misdiagnosis or a shifting of immune response with prolonged use of dupilumab.