A comparison of chest radiographs between patients with pulmonary Mycobacterium kansasii infection and those with Mycobacterium tuberculosis infection in the initial stage of disease

OBJECTIVES: To elucidate the differences in affected lung segments between patients with pulmonary M. kansasii infection and those with M. tuberculosis infection in the initial stage of disease, we examined chest radiography images and CT scans. The initial stage of disease was defined as the period when less than one-sixth of the total lung area was affected by the infection, as visualized on chest radiography and CT. SUBJECTS AND METHODS: One hundred eighty-four patients were diagnosed with M.kansasii infection between 1996 and 2010 and 835 patients, with M.tuberculosis infection between 2008 and 2009 at our hospital. The diagnosis was made on the basis of the results of sputum culture and/or bronchial washing. After excluding the patients with underlying lung diseases such as chronic pulmonary emphysema, interstitial pneumonia, and old pulmonary tuberculosis as well as those in advanced stages, 24 patients with M. kansasii infection and 62 patients with M. tuberculosis infection were included in this study. The affected segments of the lungs and the rates of cavity development were determined by using CT scans. RESULTS: In patients with M.kansasii, 17 had an infected right lung, while 7 had an infected left lung. Additionally, in patients with M.tuberculosis, 58 had an infected right lung, 3 had an infected left lung, and 1 had a bilateral infection. In patients infected with M. kansasii, the upper lobes were affected in 22 cases and the lower lobes in 3 cases. In patients infected with M. tuberculosis, the upper, middle, and lower lobes and the lingular segment were affected in 41, 8, 24, and 1 cases, respectively. Upper lobe lesions were seen more frequently in patients with M. kansasii infection than in those with M. tuberculosis infection (p < 0.05). Cavity formation was identified more frequently in patients infected with M. kansasii (91.7%) than in those infected with M. tuberculosis (32.3%) (p < 0.001). Cavitary lesions were more frequently localized to the apical, posterior, and apico-posterior regions (S1, S2 or S1 +2) of the upper lobes in patients infected with M. kansasii (86.4%) than in those infected with M. tuberculosis (35%) (p < 0.001). A solitary lesion without endobronchial spread, which is characterized by centrilobular micronodules and tree-in-bud appearance, was more frequently demonstrated in patients infected with M.ka nsasii (45.8%) than in those infected with M. tuberculosis (6.5%) (p < 0.001). CONCLUSION: Our study revealed that the apical, posterior, and apico-posterior regions of the upper lobes are vulnerable to infection by not only M.tu berculosis, but also M.ka nsasii. It is likely that M.ka nsasii might gain access to these regions via the airways and that its weak virulence may lead to higher localization.