Unmasking pulmonary actinomycosis: A diagnostic challenge in a young immunocompetent male

Pulmonary actinomycosis is a rare, indolent infection that frequently mimics pulmonary tuberculosis, malignancy, or chronic fungal disease, resulting in delayed diagnosis-particularly in regions where tuberculosis and aspergillosis are endemic.

A 33-year-old immunocompetent male presented with four months of fever, night sweats, weight loss, and progressive dry cough, followed by massive hemoptysis. Chest CT showed a cavitary right upper lobe lesion with an intracavitary ball-like component suggesting aspergilloma. Extensive microbiological investigations for tuberculosis, fungal infection, and other pathogens were negative. Due to massive hemoptysis and diagnostic uncertainty, the patient underwent VATS resection. Histopathology confirmed pulmonary actinomycosis, showing PAS-D-positive filamentous aggregates consistent with Actinomyces. He was treated with amoxicillin-clavulanate for six months, with complete radiological resolution.

This case highlights the diagnostic complexity of pulmonary actinomycosis in young immunocompetent individuals, the importance of considering it among TB and fungal mimics, and the crucial role of surgical biopsy for definitive diagnosis in complex presentations.