A case of superficial granulomatous pyoderma mimicking a basal cell carcinoma.

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis of unknown etiology with distinct clinical manifestations, frequently associated with systemic diseases. Four clinical and histological variants have been described: ulcerative, pustular, bullous, and vegetative. We report on a case of superficial granulomatous pyoderma (SGP), a vegetative form of PG, in a 40-year-old woman. Physical examination revealed an erythematous crusted plaque, measuring 2 cm in diameter, located on her left hip, which had appeared 18 months ago. Dermoscopy showed lack of pigment network, large gray-blue ovoid nests, irregular peripheral vessels, and ulceration. Laboratory examinations were normal; smears and cultures for bacteria and fungi were negative. Clinical and dermatoscopical presentation suggested basal cell carcinoma. The lesion was completely removed: histological examination showed pseudoepitheliomatous hyperplasia with intraepidermal micro-abscesses and prominent dermal inflammatory infiltrate with typical three-layered granulomas consisting of palisading suppurative granulomas surrounded by plasma cells and eosinophils (diffuse neutrophilic infiltration with dermal inflammatory infiltrates consisting of epithelioid histiocytes, lymphocytes, and multinucleated giant cells). Based on clinical and histological correlation, the diagnosis of SPG was definitively established.