The Pedal Subcutaneous Phaeohyphomycotic Cyst in an Immunocompetent Adult Man: A Case Report

Phaeohyphomycosis is a spectrum of subcutaneous and systemic infections caused by a variety of dematiaceous fungi. It is an opportunistic disease with an increased incidence in immunocompromised patients. We report a case of a pedal phaeohyphomycotic cyst in an immunocompetent adult male immigrant with the goal of highlighting its clinical presentation, diagnosis, and optimal treatment. A 57-year-old male immigrant from Panama presented with a painless, gradually increasing, large cystic lesion in his left foot, first intermetatarsal space, which had been present for many years. The patient was treated with surgical excision without antifungal therapy. Histologic analysis showed multiple granulomas composed of fibrin and necrosis in the centers surrounded by proliferative palisading fibroblasts admixed with heavily infiltrated neutrophils, plasma cells, macrophages, lymphocytes, and eosinophils. Periodic acid-Schiff and Fontana-Masson stains revealed sporadic, scattered dematiaceous fungal hyphae and pseudohyphae among granulomatous tissues. The mass was diagnosed as a phaeohyphomycotic cyst. Polymerase chain reaction-based sequencing failed to identify the fungal species because of the rarity of the fungal elements in the granulomatous tissues. The patient had no recurrence at a follow-up of 2 years. A phaeohyphomycotic cyst is a rare entity that needs to be differentiated from other benign and malignant lesions. Multiple modalities, including clinical evaluation, radiography, histologic analysis, microbiological culture, and nucleic acid sequencing, should be used for the final diagnosis. Surgical excision is an optimal treatment. Antifungal therapy should be considered based on the patient's clinical manifestation, surgical excision, and immune functional status.