Pulmonary Mycobacterium avium disease with a solitary pulmonary nodule requiring differentiation from recurrence of pulmonary adenocarcinoma.

A 56-year-old man with a past history of surgical resection of a primary pulmonary adenocarcinoma in the right upper lobe was admitted to our hospital because of a rapidly increasing solitary nodule (50x30 mm) in the right S5 followed on the chest computed tomography (CT) for three months. Although we suspected recurrence of the pulmonary adenocarcinoma and performed a CT-guided lung biopsy, we could not make a definite diagnosis. Therefore, to rule out recurrence of the primary pulmonary adenocarcinoma completely, a partial surgical resection of the right middle lobe was performed and a caseating epitheloid granuloma with acid-fast bacilli was found. As the causative pathogen, Mycobacterium avium complex (MAC) disease should be considered in the differential diagnosis of a rapidly increasing solitary nodule through this peculiar case of pulmonary MAC disease.