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Atypical (nontuberculous) mycobacteria

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 21 September 2011, last major update September 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.


● Also called nontuberculous mycobacteria (NTM)
M. avium and M. intracellulare are distinct species that cause identical disease
● Mycobacteria are separated into 4 groups in the Runyon classification (Med Clin North Am 1959;43:273, Wikipedia)

Clinical features

● Mycobacteria are present in soil and dust; are associated with domestic animals
● Associated with immunosuppression (including AIDS patients with low CD4), chronic obstructive lung disease, prior TB, pneumoconiosis, bronchiectasis, bullous emphysema, lung carcinoma (Chest 2008;133:243)
● Rarely immunocompetent patients, especially elderly females with right middle lobe involvement, cough and fatigue (“Lady Windermere syndrome", Chest 1992;101:1605)
● AIDS patients have severe infection resembling tuberculosis with impaired T-cell immunity; pulmonary involvement is part of disseminated disease
● Different organisms vary in virulence
● Radiographs show “tree in bud” opacifications
● PCR or culture required for diagnosis
Mycobacterium avium complex (MAC) is most common; also M. kansasii, marinum, gordonae, scrofulaceum, xenopi, fortuitum, chelonei, abscessus (Emerg Infect Dis 2011;17:343)

Micro description

● Marked intraalveolar and parenchymal infiltration by foamy histiocytes or proteinaceous reaction, generally without tissue destruction, lymphoid infiltrates or granulomas
● In AIDS patients, may see histiocytes packed with microorganisms without significant inflammatory response

Micro images

Mycobacterium avium complex - granulomatous inflammation

Mycobacterium avium complex - Ziehl Neelsen (acid-fast) stain (right: lymph node)

45 year old woman with COPD and mycobacterium avium complex - AFB stain

Positive stains

● Acid fast stains large numbers of intracellular bacteria; bacilli are longer (20 microns), more coarsely beaded and more bent than M. tuberculosis bacilli
● PAS positive

End of Lung-nontumor > Infections > Atypical (nontuberculous) mycobacteria

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