Multifocal subcutaneous phaeohyphomycosis: a case report with radiologic-pathologic correlation and focused literature review

Subcutaneous phaeohyphomycosis is an uncommon infection of the skin and subcutaneous tissue caused by dematiaceous (melanized) fungi, usually presenting as a solitary cystic swelling that mimics a benign cyst or bacterial abscess; multifocal disease is rare. We report the case of a 62-year-old woman with type 2 diabetes mellitus (HbA1c 7.1%) who presented with three discrete subcutaneous swellings involving the left ankle, left heel, and right forearm. Radiography, computed tomography (CT), and magnetic resonance imaging (MRI) demonstrated multiloculated cystic subcutaneous lesions with internal septations, punctate susceptibility/calcific foci, restricted diffusion, and marked perilesional edema, without osseous involvement. All three lesions were completely excised during a single procedure and submitted for histopathological examination, which showed a fibrocollagenous cyst wall with granulomatous inflammation and pigmented septate hyphae. Periodic acid–Schiff (PAS) and Grocott methenamine silver (GMS) stains were positive, confirming phaeohyphomycosis. Fungal culture and molecular identification were not performed, and the causative species was therefore not determined, which is a recognized limitation. Following excision, oral voriconazole was administered with a loading dose of 400 mg twice daily for one day, followed by 200 mg twice daily, with a planned 12-week duration and biochemical monitoring. At the time of manuscript preparation, the patient remained under scheduled follow-up; long-term recurrence data were not yet available. This case underscores that negative routine bacterial cultures or absent fungal cultures do not exclude fungal infection, that histopathology with special stains is central to diagnosis, and that radiologic-pathologic correlation and multidisciplinary care are key to managing multifocal subcutaneous phaeohyphomycosis.