Adding Another Piece to the Puzzle of Why NTM Infections Are Relatively Uncommon despite Their Ubiquitous Nature

Difficulty in Diagnosis and Management of Musculoskeletal Nontuberculous Mycobacterial Infections

We describe two cases of musculoskeletal nontuberculous mycobacterial (NTM) infection resulting in undesirable outcomes. These organisms can be difficult to identify and treat, potentially leading to significant morbidity. NTM should remain on the differential for culture negative bone and joint infections, especially with a prior surgical history or environmentally-acquired injuries.

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There is considerable difficulty in diagnosing NTM orthopedic infections.

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These infections can be prolonged and progressive.

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Consider NTM infection with negative cultures and failure of routine antibacterials.

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Surgical debridement is essential in combination with antimycobacterials.

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Treatment should be determined after culture results yield drug susceptibilities.

Histopathologic Analysis of Surgically Resected Lungs of Patients with Non-tuberculous Mycobacterial Lung Disease: a Retrospective and Hypothesis-generating Study

Non-tuberculous mycobacterial lung disease (NTM-LD) is most commonly due to species within the Mycobacterium avium complex (MAC) and Mycobacterium abscessus complex (MAbC). Surgical lung resection, typically a lobectomy or segmentectomy, is occasionally undertaken for individuals with recalcitrant but localized NTM-LD. Since the growth characteristics of MAC (slow growers) and MAbC (rapid growers) as well as their drug susceptibility patterns are significantly different, the objective of this study is to characterize and compare the histopathologic features of the resected lungs due to these two major NTM groups. From 1996 to 2017, 356 patients with NTM-LD due to MAC (n=270), MAbC (n=54), or both (n=32) underwent a total of 404 lobar resections (with the lingula counted as a separate lobe) at the University of Colorado Hospital. We analyzed by microscopy the existing surgical lung tissue sections for bronchiolitis, bronchiolectasis, bronchiectasis, non-necrotizing granuloma (airway, parenchymal, and total), necrotizing granuloma (airway, parenchymal, and total), peri-airway fibrosis, fibrous pleuritis, and lymphoid follicles. There were no significant differences in the presence or absence of most of the histopathologic features of surgically removed lungs due to MAC, MAbC, or both MAC + MAbC. However, there were significantly more necrotizing granulomas (airway, parenchymal, and total) and fibrous pleuritis in MAC compared to MAbC lung diseases. Since necrotizing granulomas may be a sign of inadequate control of the infection, we posit that their presence may be an indication of increased chronicity, increased virulence of MAC compared to MAbC, and/or impaired host immunity against the NTM. Futures studies to determine the root cause of such differences in histopathologic findings in MAC versus MAbC lung disease may spawn new leads on differential pathogenic mechanisms with different NTM, with the goal of aiming for more targeted therapy against both the NTM and the lung damage induced by them.