Neutrophilic Fixed Drug Eruption Mimicking Neutrophilic Dermatosis: Two Cases, Including Sequential Biopsies Demonstrating Time-Dependent Histopathology.

Fixed drug eruption (FDE) is classically a lymphocyte-predominant interface dermatitis, but an early lesion may show a prominent neutrophilic infiltrate that closely simulates a primary neutrophilic dermatosis. We report 2 cases. The first, a 42-year-old woman, developed a multifocal eruption approximately 45 minutes after re-exposure to etoricoxib, recurring at previously affected and new sites. A punch biopsy performed 21 hours after ingestion of the drug showed a basketweave stratum corneum, intense papillary dermal edema with pseudovesiculation, and a superficial and deep infiltrate rich in neutrophils with karyorrhexis, closely resembling Sweet syndrome. Only occasional apoptotic keratinocytes were present within the epidermis, and the marked edema obscured any interface dermatitis, although admixed eosinophils were noted. Clinicopathologic correlation ultimately established the diagnosis of neutrophilic FDE. The second, a 55-year-old man, had an eruption recurring at the same sites after pseudoephedrine. A biopsy of an established lesion 2-3 weeks after ingestion showed classic interface dermatitis with numerous eosinophils and pigment incontinence, whereas one taken from the same region within 24 hours of re-exposure showed a neutrophil-predominant infiltrate with prominent karyorrhexis and only focal interface change. These cases, biopsied at documented time points, support the concept that the neutrophil-rich appearance of FDE represents an early phase in its histopathologic evolution, demonstrate how it can be mistaken for a neutrophilic dermatosis in the absence of adequate clinical history, and show that clinicopathologic correlation and a high index of suspicion are necessary to reliably arrive at the correct diagnosis.