Rationale: Existing literature is inconclusive regarding how the nodular bronchiectatic form of Mycobacterium avium complex (MAC) disease will progress without treatment and when treatment initiation should be considered.
Objectives: To assess the natural course of MAC pulmonary disease by serial thin-section computed tomography (CT).
Methods: Of 339 patients with nodular bronchiectatic form of MAC disease, we selected 265 untreated patients who had serial CTs (mean observation period, 32 ± 21 mo). Two independent chest radiologists reviewed retrospectively all CT scans for the presence and extent of lung abnormalities (maximal total score, 30).
Measurements and main results: Of 265 patients, 126 patients (48%) had disease that had progressed and that needed treatment owing to radiologic deterioration or worsening symptoms, and the remaining 139 patients (52%) did not. On multivariate analysis, the presence of cavity (adjusted hazard ratio, 2.06; P = 0.004) and consolidation (adjusted hazard ratio, 1.55; P = 0.019) at initial CT remained as independent factors associated with disease progression and treatment requirement. The presence of cavitary lesions demonstrated the highest positive predictive value (61%) and significant correlation (P = 0.005) with smear positivity. Differences in the extent of each pattern and total CT score in the serial studies were significantly larger (P < 0.05) in patients requiring treatment. The total CT score increased by 2.41 in the treatment-requiring group compared with 0.25 in the group that did not receive treatment.
Conclusions: Without treatment, about half of patients demonstrate progressive disease on serial CT over a mean follow-up period of 32 months and, thus, required treatment. Patients showing cavities or consolidation on initial CT are more likely to have progressive disease and thus to require treatment eventually.