Fungal Osteomyelitis Due to Naganishia Albidus in an Immunocompetent Patient

Osteomyelitis is a bone infection most commonly caused by bacteria, but fungi may also be causative agents. Fungal osteomyelitis usually occurs in immunosuppressed patients or is associated with invasive devices; however, here we report a case of fungal osteomyelitis in an immunocompetent patient. A 33-year-old man from the western zone of Rio de Janeiro was diagnosed with pulmonary tuberculosis in September 2024 based on sputum testing and started treatment. After one month, he developed left ankle swelling and was admitted to a municipal hospital. Ankle CT showed bone destruction with an associated abscess, and after surgical intervention, Acinetobacter baumannii was isolated and treatment was started, but without clinical or imaging improvement. He was transferred to another public hospital and showed signs of disseminated disease, including dyspnea, weight loss, and severe joint pain, associated with drainage from the ankle lesion and a new lesion over the clavicle. CT revealed multiple abscesses in the thyroid and lung, and bone scintigraphy showed disseminated lytic lesions. Workup for congenital and acquired immunodeficiencies was negative. Surgical procedures were performed on the ankle and clavicle, as well as bronchoscopy. Soft tissue culture from the ankle grew Naganishia albidus (formerly Cryptococcus albidus). Tests for bacteria and mycobacteria were negative, and histopathology of the ankle bone fragment described a “non-caseating granulomatous reaction composed of aggregates of epithelioid histiocytes and multinucleated Langhans-type giant cells, without evidence of central necrosis. Stains for mycobacteria and fungi negative.” Other specimens (bronchoalveolar lavage and bone fragments) were negative. He was treated with amphotericin B for 28 days, with marked clinical and CT improvement, as well as complete healing of the ankle and clavicle lesions. Oral itraconazole was continued, with no new signs of active disease. Fungal osteomyelitis is rare in immunocompetent patients, especially due to the albidus species. This case reinforces the importance of pursuing an etiologic diagnosis in osteomyelitis and the need to investigate pathogens beyond bacteria, even in cases that do not initially suggest uncommon diseases.