Pulmonary Actinomycosis Mimicking Lung Cancer: A Case Report of a Rare Imitator.

Pulmonary nodules mimicking lung cancer pose a significant diagnostic challenge due to overlapping clinical and radiological features, which frequently lead to referrals to chest clinics for further evaluation. A 73-year-old man presented to the chest clinic with a two-month history of fatigue, loss of appetite, and unintentional weight loss. Computed tomography (CT) scan of the chest revealed suspicious soft tissue lesions in the left upper and right middle lobes of the lungs. His medical history was notable for colorectal adenocarcinoma, treated with a right hemicolectomy in 2012, followed by adjuvant chemotherapy in 2018. A diagnostic dilemma arose when colonoscopy was inconclusive, and both pulmonary nodules demonstrated increased fluorodeoxyglucose uptake on positron-emission tomography scan, suggestive of lung malignancy. However, an initial CT-guided biopsy of the left upper lobe pulmonary nodule was nondiagnostic, and there was no evidence of recurrence of colorectal carcinoma. The diagnosis was ultimately established following a wedge resection of the right middle lobe pulmonary nodule, with histopathological analysis confirming pulmonary actinomycosis. The pulmonary nodules completely resolved after a prolonged course of antibiotics. Pulmonary actinomycosis is a rare granulomatous infection caused by the gram-positive anaerobe Actinomyces spp. Diagnosis is often delayed due to its uncommon presentation as pulmonary nodules and its ability to mimic malignancy. This case highlights the importance of including pulmonary actinomycosis in the differential diagnosis of pulmonary nodules to avoid delays in appropriate treatment.