Pulmonary Mycobacterium avium complex (MAC) disease showing middle lobe syndrome--pathological findings of 2 cases suggesting different mode of development]

Two different processes have been proposed for pathogenesis of Mycobacterium avium complex (MAC) disease which show the middle lobe syndrome: 1) middle lobe bronchiectasis followed by MAC infection and 2) MAC disease resulted in secondary bronchiectasis. Two surgical specimen from MAC cases showing middle lobe syndrome were studied histo-pathologically. The first case was a 60 year-old female with frequent bloody sputum, who had been diagnosed as bronchiectasis in her childhood. Pathological examination of the resected middle lobe showed prominent cylindric bronchiectasis in the indurated middle lobe, and epithelioid cell granulomas were scattered limited to the fibrous bronchial walls, without any granulomas in the lung parenchyma. These findings suggested a secondary infection of MAC to the non-specific pre-existed bronchiectasis. The second case of a 55 year-old female having repeated bloody sputum, who was diagnosed to be tuberculosis but no improvement with anti-tuberculosis drugs. Pathological examination of the middle lobe showed scattered epithelioid cell granulomas with lymphocytic infiltration in the lung parenchyma. A few epithelioid cell granulomas were also found in the mucosa of middle lobe bronchi. In this case, pulmonary MAC lesions seemed to precede the central bronchial lesion with later development of bronchiectasis. Summarizing above findings two different mode of pathogenesis ways may be considered; one is non-specific bronchiectasis followed by middle lobe MAC disease and the other is pulmonary MAC lesion in the middle lobe as a primary change.