Background/Purpose: Pulmonary MAC disease is caused by MAC and the incidence is increasing in Japan. It is also becoming a great concern in the field of rheumatology because there are no drugs which show good anti-MAC activity. Another problem is diagnostic criteria for pulmonary MAC disease that has been revised many times, in which positive sputum culture more than twice is included. However, it takes long time to get culture positive twice. Measurement of anti-MAC antibody was developed by Kitada, et al (Am J Respir Crir Care Med 2008) and is commercially available (Capilia MAC, TM), and the sensitivity has been reported to be 70 – 80 % with very good specificity. We aimed to detect risk factors for pulmonary MAC disease in patients with rheumatic diseases and the significance of the measurement ant-MAC antibody.

Methods:  Subjects were 88 patients with various rheumatic diseases whose chest CT findings showed small nodular opacities, bronchiectasis, and, in cases, cavities which are difficult to distinguish from pulmonary lesions due to rheumatic diseases itself. Sputum culture was done more than twice, and blood was drawn for anti-MAC antibody detection. PCR test for MAC in sputum samples was done in most of the patients. Fourteen clinical factors, such as age, gender, BMI, underlying diseases, dose of PSL and MTX, and others, were collected and multivariate analysis was done to find risk factors of pulmonary MAC disease.

Results: Out of 88 patients, 12 patients fulfilled the criteria for pulmonary MAC disease. However, 2 patients showed sputum culture positive once and PCR test for MAC in another sample was positive, and these patients were treated as pulmonary MAC disease resulting in good response. Therefore, we included these 2 patients into pulmonary MAC disease. Multivariate analysis found only one significant risk factor, low BMI. The mean BMI with and without pulmonary MAC disease were 17.5 +/- 2.3 and 21.3 +/- 3.7, respectively (p < 0.0005). In patients with BMI less than 18.5, OR of developing pulmonary MAC diseases was 12.3. Anti-MAC antibody was positive in 11 patients. In 14 patients diagnosed as pulmonary MAC disease, ant-MAC antibody was positive in 9, and 2 patients not diagnosed as MAC disease were positive for anti-MAC antibody. The sensitivity, specificity, PPV and NPV of ant-MAC antibody for pulmonary MAC disease were 64.3 %, 97.3 %, 81.8 %, and 93.9 %, respectively.

Conclusion: Low BMI was only one risk factor of developing pulmonary MAC disease in patients with rheumatic diseases, which is consistent with that in general populations. Measurement of anti-MAC antibody can be a replacement of one positive sputum culture, but further study is definitely needed.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/risk-factors-of-pulmonary-mycobacterium-avium-comlex-mac-disease-and-the-significance-of-anti-mac-antibody-in-patients-with-rheumatic-diseases/