[A case of pulmonary dirofilariasis that required differentiation from nontuberculous mycobacteriosis].

A 48-year-old man was admitted with an abnormal shadow on a chest X ray. Chest X ray and CT revealed a solitary nodule in the right lung field. Mycobacterium gordonae was cultured from sputum. Tumorectomy by video-assisted thoracoscopic surgery was done for histological diagnosis, and Dirofilaria worms accompanied with epithelioid cell granuloma with necrosis were found, while no bacteria were cultured from biopsy specimen, thus we diagnosed dirofilariasis. Because a solitary nodule can be caused by either Dirofilaria species or nontuberculous mycobacteria, this case was of interest with regard to the differential diagnosis of a lung solitary nodule.