Computed tomographic abnormalities in Mycobacterium avium complex lung disease include the mosaic pattern of reduced lung attenuation

Objective: To describe the range and frequency of abnormalities on computed tomographic (CT) scans in patients who met the American Thoracic Society ( ATS) case definition of Mycobacterium avium complex (MAC) lung disease. Fur ther, to report the effect of time and treatment on the progression of thes e abnormalities. Methods: The demographic, clinical and radiologic features of 10 patients with proven MAC lung disease (mean age 71 years, standard d eviation 12 years) were described. The presence or absence of 14 CT abnorma lities was recorded in each of 10 lung zones. The effects of time and treat ment on the abnormalities were recorded. Results: The patients' lung functi on was minimally impaired. Pretreatment CT scans showed small nodules in 47 % of the lung zones, reduced lung attenuation in 41%, and bronchiectasis in 27%. Bronchiectasis was associated with nodules in 20 zones from 9 patient s and with no nodules in 7 zones from 1 patient. Reduced attenuation was as sociated with bronchiectasis alone in 8 zones, with nodules alone in 25 zon es and with both bronchiectasis and nodules in 8 zones. In patients without treatment, or with non-curative treatment, bronchiectasis developed or wor sened in 12 of 26 zones and resolved or improved in none. In contrast, afte r curative treatment, small nodules disappeared completely in 10 of 21 zone s and developed in none. Of 7 zones with only nodules and reduced attenuati on before treatment, 6 had no abnormalities after treatment. Conclusions: O ur data suggest that the 3 leading CT abnormalities in nodular-bronchiectat ic MAC lung disease are small nodules, reduced attenuation and bronchiectas is. Reduced attenuation appeared to result from gas trapping and hypoxic va soconstriction due to bronchiolocentric inflammatory nodules. Bronchiectasi s appeared to be secondary to this bronchiolar disease.