Nellya Ablayeva

Title: Cutaneous botryomycosis of the foot mimicking a soft tissue neoplasm in an immunocompetent adult

Abstract

Botryomycosis represents a rare, persistent, pyogranulomatous bacterial pathology that manifests with visceral and cutaneous inflammatory lesions. Because it mimics mycetoma and actinomycosis clinically, histologically, and radiologically, the disease may be underdiagnosed, particularly in the distal extremities. We report a 33-year-old immunocompetent man referred from podiatry with a 10-year history of a nodular mass with a draining yellow-red sinus on the dorsum of the right foot, now progressively swollen and painful, along with hyperpigmented plaques and nodules on the left knee. Initial clinical and radiologic assessment favored mycetoma or a soft-tissue tumor; MRI suggested desmoid-type fibromatosis, dermatofibrosarcoma protuberans, or atypical vascular malformation. Empiric broad-spectrum antibiotics were initiated but then deliberately discontinued in this clinically stable patient to preserve the diagnostic yield of biopsy and cultures. Incisional biopsies of the right foot showed a pyogranulomatous infiltrate with botryoid granules; Gram staining demonstrated gram-positive cocci in clusters and negative special stains (PAS, GMS, Fite, AFB). Aerobic wound cultures grew oxacillin-susceptible Staphylococcus aureus, establishing the diagnosis of cutaneous botryomycosis. The patient improved with targeted oral trimethoprim–sulfamethoxazole and local wound care, with surgical debulking reserved for residual disease. This case highlights botryomycosis as an essential consideration in chronic extremity masses with draining sinuses, even in immunocompetent hosts. It underscores the diagnostic value of temporarily withholding antibiotics in selected stable patients.