Objective: The purposes of this study were to describe and compare the prevalence of disease features in subjects with Mycobacterium avium complex (MAC) disease with those of Mycobacterium tuberculosis infection (MTB), to compare the abilities of CT and chest radiography to identify the features of MAC disease, and to determine if sputum positivity is related to any of the CT features of MAC disease.
Methods: Computed tomographic scans of 15 subjects with MTB and 55 subjects with MAC were reviewed by 2 observers. Sputum culture results (obtained within 1.9 +/- 2.8 days of scanning) were available in 50 of the 55 subjects with MAC.
Results: Bronchiectasis involving four or more lobes (often associated with centrilobular nodules) was seen only in subjects with MAC. The combination of right middle lobe and lingular bronchiectasis was seen only in MAC (p = 0.015). Thirty-one of the 34 subjects (91%) with MAC who had cavities on CT had a positive sputum culture within 3 weeks of CT, compared with 7 of 12 subjects (58%) without cavities (p = 0.001). Similarly, 36 of 42 subjects (85%) with airspace disease, but only 2 of 8 subjects (25%) without airspace disease grew mycobacteria from their sputa (p < 0.001). Sputum positivity was not associated with the presence of bronchiectasis (p = 0.156) or nodules (p = 0.377).
Conclusion: A subgroup of patients with MAC may be distinguished from those with MTB by the presence of widespread bronchiectasis, particularly if it involves the right middle lobe and lingula. Cavities and airspace opacification on CT are associated with positive sputum cultures for MAC.