Lung - nontumor
Atypical (nontuberculous) mycobacteria

Topic Completed: 1 September 2011

Revised: 29 January 2019, last major update September 2011

Copyright: (c) 2003-2017,, Inc.

PubMed search: atypical [title] OR nontuberculous [title] mycobacteria lung

Elliot Weisenberg, M.D.
Page views in 2019: 3,419
Page views in 2020 to date: 776
Cite this page: Weisenberg E. Atypical (nontuberculous) mycobacteria. website. Accessed April 1st, 2020.
  • 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)
Microscopic (histologic) 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
Microscopic (histologic) images

Images hosted on other servers:

Mycobacterium avium complex - granulomatous inflammation

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

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
Back to top