[Pathological characteristics and molecular diagnosis of non-tuberculosis Mycobacterium lung disease]

Objective: To investigate the clinicopathological features of non-tuberculosis mycobacterial lung disease and the role of molecular pathology in diagnosis. Methods: Forty-five formalin-fixed, paraffin embedded (FFPE) specimens were collected from the Department of Pathology, Beijing Chest Hospital from February 2016 to August 2019. The clinical, imaging and histopathologic features, bacteriologic data and morphologic characteristics of acid fast bacilli (AFB) were analyzed retrospectively. Specific gene sequence IS6110 of Mycobacterium tuberculosis (MTB) was detected by fluorescence PCR. Identification of Mycobacteria was by melting curve method. Fifty cases of pulmonary tuberculosis were selected in the same period as control. Results: The NTM lung cases included 18 cases (40.0%, 18/45) of M. intracellulare, eight cases (17.8%, 8/45) of M. xenopi, six cases (13.3%, 6/45) of M. avium, six cases (13.3%, 6/45) of M. kansasii, six cases (13.3%, 6/45) of M. chelonae and one case (2.2%, 1/45) of M. simiae. Histopathologically, there were necrotizing granulomas in 34 cases (75.6%, 34/45), non-necrotizing granuloma in one case (2.2%, 1/45) and non-granulomatous lesions in 10 cases (22.2%, 10/45). The necrosis was pink necrosis, basophilic necrosis rich in nuclear fragments and suppurative necrosis. Pulmonary TB showed more pink necrosis and basophilic necrosis, the difference was statistically significant (χ(2)=10.270, P=0.001; χ(2)=7.449, P=0.006). Seventeen cases (37.8%, 17/45) of NTM lung disease showed giant multinucleated giant cells, which were significantly different from those in pulmonary tuberculosis group (χ(2)=13.446, P<0.01). The number and morphology of AFB were also different. More AFB were found in M. intracellular cases and significant AFB were easily seen in M. kansasii infection. Conclusions: M. tuberculosis and NTM cannot be reliably differentiated by histologic features or by AFB morphology. Molecular assays are important to distinguish tuberculosis from NTM lung disease.