[Clinical features of the patients with "secondary infection" of Mycobacterium avium complex--Radiographic pattern of progressions in the patients with and without underlying pulmonary conditions].

We reviewed the radiographic features of 42 patients with Mycobacterium avium complex (MAC) infection. Six cases were definite "primary", 20 were "secondary", and 15 were indeterminate (probably "primary"). In the definite and probable "primary" cases, and some of the "secondary" cases, pulmonary lesions slowly progressed following a common and characteristic sequence from a cluster of small nodules or fibro-productive nodules to those with subpleural thickening, or with thickening of the draining bronchi, or with both subpleural and bronchial thickening, and to cystic bronchiectatic changes associated with collapse of the segment or the lobe, in the final stage. Cases of airspace pneumonia appeared rarely. In these cases, neither apical-subapical region prevalence, pleural effusion, nor mediastinal lymphadenopathy were found. On the contrary, in five cases of "secondary" infection, MAC lesions located at the same place with the predisposing lung disease and did not progress during more than five years of observation. In the progressive cases of "secondary" infection, however, the appearance of new lesions and the progressions thereafter showed the same pattern as in "primary" infection. These features would suggest that MAC infection would occur and progress slowly among patients who had unknown pathogenetical factor, whether they had underlying predisposing lung conditions or not.