BACKGROUND: Pulmonary actinomycosis is an uncommon infection with nonspecific clinical and radiologic features that can be difficult to distinguish from lung malignancy, tuberculosis, and other chronic pulmonary diseases. This report describes a patient with pneumoconiosis in whom bronchoalveolar lavage fluid (BALF) metagenomic next-generation sequencing (mNGS) provided important microbiologic evidence to support the diagnosis of pulmonary actinomycosis after inconclusive conventional evaluation.

CASE REPORT: A 53-year-old nonsmoking presented with a 1-month history of cough and hemoptysis. Chest computed tomography showed bilateral upper-lung masses, multiple nodules, and lymphadenopathy; he initially underwent right upper lobectomy because malignancy was suspected. Histopathologic examination showed necrotizing granulomatous inflammation with carbon deposition, but no specific pathogen was identified. Empirical antituberculosis treatment was ineffective. After transfer to our hospital, bronchoscopy was performed. Routine BALF culture and staining results were negative, whereas mNGS detected Actinomyces israelii. Intravenous ampicillin/sulbactam led to clinical and radiologic improvement, but severe thrombocytopenia developed. Platelet counts decreased again after subsequent penicillin exposure, supporting probable penicillin-induced thrombocytopenia. After discontinuation of penicillin and joint evaluation by respiratory physicians and clinical pharmacists, omadacycline was administered, followed by oral doxycycline. The patient displayed clinical improvement, platelet counts normalized, and follow-up imaging showed lesion absorption.

CONCLUSIONS: This case illustrates the diagnostic difficulty of pulmonary actinomycosis in a patient with pneumoconiosis and suggests that BALF mNGS can be helpful when routine studies are unrevealing. It also indicates that omadacycline is a feasible alternative when penicillin-associated thrombocytopenia prevents continuation of first-line therapy.

Keywords: Pneumoconiosis, Thrombocytopenia, Actinomycosis