Abstract
Background: We occasionally experienced cases suspected of pulmonary Mycobacterium avium complex (MAC) by radiological findings without positive bacterial cultures. In this study, we evaluated features of pulmonary MAC cases diagnosed later in the follow-up after negative close investigation.
Methods: We defined two groups of pulmonary MAC cases; first study negative (FSN) group and first study positive (FSP) group. The FSN group consisted of patients whose first close examinations including bronchial washings revealed negative for MAC isolation, but turned positive later in the follow-up studies. The first examination was performed between 2007 and 2011 in our hospital. On the other hand, the FSP group consisted of patients with positive MAC cultures in the first study between 2007 and 2011.
Results: We recruited 24 patients in the FSN group and 266 patients in the FSP group. Radiological findings were categorized into four entities; isolated mass (n=7 in FSN, n=6 in FSP), nodular/bronchiectasis (NB) (n=17 in FSN, n=245 in FSP), fibrocavitary (FC) type (n=0 in FSN, n=9 in FSP), and others (n=0 in FSN, n=6 in FSP). The FSN group exhibited more “isolated mass” cases (p<0.001) and less NB type (p<0.001). When limited to NB type patients, FSN group showed less cavitations (FSN 6% vs FSP 32%; p=0.04).
Conclusion: Pulmonary MAC patients with an isolated mass were difficult to diagnose by proving mycobacteria with bronchial washings. MAC tended to be isolated in the first study of FC type and NB type especially NB type with cavities.
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