Organizing pneumonia due to actinomycosis: an undescribed association.

Organizing pneumonia is a pathologic entity characterized by intra-alveolar buds of granulation tissue that can extend to the bronchiolar lumen. It is a non-specific finding reflecting a pattern of pulmonary response to aggression that can be cryptogenic or associated with several causes. Pulmonary actinomycosis is a rare infectious disease, of bacterial aetiology, and of difficult diagnosis. This disease usually causes non-specific respiratory symptoms and radiological findings, and the treatment is based on the use of antibiotics. The authors describe a clinical case of a 53-year-old male smoker (50 pack years), initially seen for complaints of right-sided chest pain and sub-febrile temperature. Imaging studies revealed a mass in the inferior right lobe and enlarged mediastinal lymph nodes. Empirical treatment with antibiotics caused partial and temporary improvement. Transthoracic biopsy revealed a pattern of organizing pneumonia with giant multinucleated cell granulomas. Repeat imaging studies revealed an enlargement of the pulmonary mass and therefore a right inferior lobectomy was performed. The pathologic study revealed a histological pattern of organizing pneumonia surrounding inflammatory bronchiectasis with a large number of Actinomyces colonies. To our knowledge there is presently no report in the literature of organizing pneumonia associated with Actinomyces infection.