Clinical features and treatment outcomes of pulmonary actinomycosis

Pulmonary actinomycosis is a rare and chronic infectious disease that mimics malignancy and is frequently misdiagnosed. There are few reports that address the clinical characteristics of pulmonary actinomycosis. The objective of this research is to evaluate the clinical features, radiological findings, diagnostic approaches and treatment outcomes of pulmonary actinomycosis.

Thirty-seven patients with pulmonary actinomycosis histopathologically diagnosed from 2009 to 2021 were analyzed retrospectively.

The mean age at presentation was 53.7 (±13.3) years. Frequent symptoms were cough and hemoptysis. The median diagnosis time from the first symptoms was 60 days (interquartile range 18-195). Pulmonary comorbidity was found in 59.5% of cases. The most common thorax computed tomography finding was mass or nodule. The low-attenuation center within the mass or consolidation was observed in 40% of the lesions. The median maximal standardized uptake value of lesions on positron emission tomography (PET) was 6.5 (interquartile range 2.7-10.3). In the majority of cases (97.3%), the diagnosis of pulmonary actinomycosis was not suspected at admission, and 56.8% of patients were misdiagnosed with lung cancer. The mean duration of antibiotic therapy was 9.4 days (range 3-22) with intravenous antibiotics and 64.7 days (range 5-270) with oral antibiotics. Four patients died due to concomitant comorbidities. Eight cases were lost to follow-up. All other cases were fully cured.

Pulmonary actinomycosis mimics other diseases, often lung cancer. Clinicians should consider the diagnosis of actinomycosis when they detect a mass or consolidation, especially with a low-attenuation center. PET/CT appears not to be useful for differential diagnosis. A shorter course of antibiotic therapy than traditionally recommended appears to be sufficient.