Vegetative Pyoderma Gangrenosum Mimicking Squamous Cell Carcinoma: A Poorly Recognized Diagnostic Challenge.

Abstract: Pyoderma gangrenosum (PG) is a rare inflammatory neutrophilic dermatosis that is difficult to diagnose due to non-specific clinical, laboratory, and histopathologic features. Distinguishing pseudoepitheliomatous hyperplasia (PEH) from squamous cell carcinoma (SCC) is also histopathologically challenging. The connection between PEH and PG is not well recognized, and instances of PG mimicking SCC are rare. We report a case of vegetative PG accompanied by PEH, originally mistaken for SCC. A 78-year-old woman presented with a 3-month history of an ulcerated, exophytic, and painful mass on her right lower leg. An incisional biopsy revealed PEH and neutrophilic microabscesses, initially raising concerns for SCC keratoacanthoma type with PEH or well-differentiated, infiltrative SCC. However, following additional review of clinical and histopathologic findings at the cutaneous oncology tumor board, the diagnosis of vegetative PG with associated PEH was favored. This case highlights the significance of recognizing PEH as a histopathology feature that can be seen in PG and lead to difficulty distinguishing PG with PEH from SCC. We stress the importance of promptly diagnosing PG through clinical and histopathologic correlation to prevent diagnostic delays and unnecessary surgeries or treatments.