Abstract

Distinguishing severely atypical keratoacanthoma (KA) from keratoacanthoma-like squamous cell carcinoma (SCC) has been widely debated in the literature. While some favor KA to be a benign process, some argue they are a variant of SCC. The distinction, however, can have great consequences, as some KAs originally thought to be benign have been reported to metastasize and take on an aggressive behavior. Furthermore, the distinction will likely be used to guide clinical management. Immunohistochemistry has often been used to differentiate between these entities. A 72-year-old male presented to dermatology with diffuse erythematous scaly plaques serpiginous borders. Punch biopsies were performed that demonstrated spongiotic and slightly psoriasiform dermatitis with eosinophils. The patient was empirically treated with permethrin 5% cream and triamcinolone 0.1% cream. One month follow-up showed his rash improved clinically, however he was found to have a new eruption of excoriated nodules scattered over his scalp, upper extremities, and back. Two additional punch biopsies were performed that revealed atypical squamous proliferations with keratoacanthoma-like features. Invasive squamous cell carcinoma was favored from the histologic appearance, though due to the unusual clinical history, immunohistochemistry was performed. Lesions stained positive for Ki67 and p53 showed wild-type pattern. CD30 stain was performed due to the rare occurrence of keratoacanthomas in CD30 lymphoproliferative disorders, but was negative. Due to the staining pattern and clinical history, a diagnosis of eruptive KAs was made. Patient was treated with intramuscular triamcinolone and oral prednisone with subsequent resolution of his lesions, further supporting the diagnosis of eruptive KAs.

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