Pulmonary Mycobacterium avium infection demonstrating unusual lobar caseous pneumonia

Mycobacterium avium complex (MAC) infection is a major medical concern in Japan because of its increased prevalence and associated mortality. A common radiological feature in pulmonary MAC infection is a mixture of two basic patterns: fibrocavitary and nodular bronchiectatic; however, lobar consolidation is rare. We report an 83‐year‐old man with lobar caseous pneumonia caused by pulmonary MAC infection. Radiological findings were predominantly composed of dense lobar consolidation and ground‐glass opacity. A diagnosis was made in accordance with the clinical and microbiological criteria set by the American Thoracic Society. A histological examination of lung specimens obtained by using a bronchoscope revealed a caseous granulomatous inflammation with an appearance of Langhans cells. The patient was treated using combined mycobacterium chemotherapy with an initial positive response for 6 months; however, the disease progressed later. We suggest that an awareness of lobar pneumonic consolidation as a rare radiological finding in pulmonary MAC infection is important.