eMedicine Specialties > Radiology > Chest
Lung, Nontuberculous Mycobacterial Infections
Updated: Apr 3, 2008
Introduction
Background
Images in a 50-year-old man with chronic obstructive pulmonary disease (COPD), a worsening cough, and a low-grade fever of 3 months' duration show cavitating consolidation and volume loss, the primary pattern associated with nontuberculous mycobacterial infections. This particular patient had a Mycobacterium kansasii infection.
Chest CT scans in a patient with Mycobacterium avium-intracellulare complex (MAI complex) infection show nodules and multifocal bronchiectasis in the middle lobe and lingula.
Nontuberculous mycobacteria (NTM) are environmental organisms that are normally found in soil and water. They have only recently been associated with disease. In 1968, Dr Wolinsky published the first comprehensive review, stating, "chronic pulmonary disease resembling tuberculosis [TB] represents the most important clinical problem associated with NTM."1 Since then, a variety of manifestations of NTM infection have been described, but the lungs remain the most commonly involved site.
Pathophysiology
The best-studied NTM are Mycobacterium avium-intracellulare complex (MAI complex) and Mycobacterium kansasii. Nontuberculosis mycobacteria are pathogenic mycobacteria, other than Mycobacterium leprae, that are not part of the tuberculosis complex. There are many other potentially pathogenic NTM organisms.
Chronic pulmonary disease remains the most common localized manifestation of infection. MAI complex is the most common pathogen in the US, followed by M kansasii, whereas MAI complex and then Mycobacterium xenopi are most common in Canada and in parts of Europe.
Aerosolized water is currently believed to be the most likely source of infection.2 Human-to-human or animal-to-human transmission is rare. Human disease is correlated with the geographic concentration of NTM. That is, MAI complex is commonly seen in southeast parts of the US, whereas M kansasii is more common in the Midwest. The initial site of entry is probably the lung; granulomatous inflammation is the key pathologic feature. Disseminated disease associated with HIV may be secondary to the oral ingestion of contaminated water.3,4
Related eMedicine topics:
Mycobacterium Kansasii
Mycobacterium Avium-Intracellulare
Frequency
United States
NTM infection is not a reportable disease in the US, and the exact prevalence is not known.5 Currently, more isolates are of MAI complex than of Mycobacterium tuberculosis (MTB). MAI complex is the most common pathogen in the US, followed by M kansasii, but the frequency is certainly dependent on the particular patient population.
International
In Canada and Europe, MAI complex is most common, followed by M xenopi.
Mortality/Morbidity
Mortality is an uncommon outcome of NTM infection in nonimmunocompromised patients.
Race
NTM infections appear to be more prevalent in whites, excluding patients with AIDS. The reason for this is not known.
Sex
Two typical patterns of NTM infections of the lung have been noted. Elderly males with chronic obstructive pulmonary disease (COPD) are more commonly affected with the more prevalent pattern that mimics TB, whereas middle-aged to elderly women characteristically have focal bronchiectasis and scarring in the absence of underlying pulmonary disease.
Age
See Sex, above.
Presentation
The diagnosis of NTM infection can be made in the presence of the following: (1) clinical signs and symptoms compatible with mycobacteriosis, (2) compatible chest radiographic or high-resolution computed tomographic (HRCT) findings (see CT Scan below), and (3) isolation of NTM from respiratory specimens on more than 1 occasion (see American Thoracic Society guidelines for details).3,6,7
Patients with underlying lung disease or immunosuppression are at highest risk for infection. However, immunocompetent subjects are also susceptible to the disease.8,9,10 Clinically, the major symptoms are similar to those associated with TB—namely, cough, hemoptysis, fever, night sweats, and/or weight loss. The clinical presentation is generally independent of the species, but M kansasii is thought to behave more like TB than the others. Most infections are related to MAI complex, except in certain areas where M kansasii is predominant.
The reliable diagnosis or exclusion of the disease is difficult in many cases despite use of the guidelines mentioned above.
In immunocompromised patients who have a clinically high likelihood of NTM disease, infection may be presumed with any isolation of NTM in respiratory specimens. In contrast, more stringent proof, such as pathologic specimens demonstrating granulomas and/or acid-fast bacilli, may be appropriate in unusual clinical settings.
As always, other diseases should be excluded before the diagnosis is made, and the absence of a response to therapy should prompt reassessment. The isolation of NTM from tissues where contamination is unlikely is usually considered proof of disease. Treatment should be tailored to the particular strain isolated; adequate therapy usually results in a good clinical response.11
Preferred Examination
The increasing efficiency of microbiologic laboratories in isolating small quantities of organisms has made the distinction between colonization and infection more difficult. Therefore, diagnostic guidelines from the American Thoracic Society suggest that the presence of symptoms and radiographic evidence of infiltrates (nodular or cavitary disease) are an essential adjunct for the microbiologic diagnosis.3,6
Limitations of Techniques
No single test, including microbiologic tests, yields results diagnostic of NTM infections.
Differential Diagnoses
Bronchiolitis Obliterans Organizing
Pneumonia
Lung, Postprimary Tuberculosis
Lung, Primary Tuberculosis
Pneumonia, Atypical Bacterial
Pneumonia, Viral
Sarcoidosis, Thoracic
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| References |
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References
Wolinsky E, Rynearson TK. Mycobacteria in soil and their relation to disease-associated strains. Am Rev Respir Dis. Jun 1968;97(6):1032-7. [Medline].
Wallace RJ Jr. Nontuberculous mycobacteria and water: a love affair with increasing clinical importance. Infect Dis Clin North Am. 1987;1(3):677-86.
ATS. Diagnosis and treatment of disease caused by nontuberculous mycobacteria. This official statement of the American Thoracic Society was approved by the Board of Directors, March 1997. Medical Section of the American Lung Association. Am J Respir Crit Care Med. Aug 1997;156(2 Pt 2):S1-S25. [Medline].
Glassroth J. Pulmonary disease due to nontuberculous mycobacteria. Chest. Jan 2008;133(1):243-51. [Medline].
Khan K, Wang J, Marras TK. Nontuberculous Mycobacterial Sensitization in the United States: National Trends over Three Decades. Am J Respir Crit Care Med. Aug 1 2007;176(3):306-13. [Medline].
Griffith DE, Aksamit T, Brown-Elliott BA, Catanzaro A, Daley C, Gordin F. An official ATS/IDSA statement: diagnosis, treatment, and prevention of nontuberculous mycobacterial diseases. Am J Respir Crit Care Med. Feb 15 2007;175(4):367-416. [Medline].
Griffith DE, Brown-Elliott BA, Wallace RJ Jr. Diagnosing nontuberculous mycobacterial lung disease. A process in evolution. Infect Dis Clin North Am. 2002;16(1):235-49. [Medline].
Guide SV, Holland SM. Host susceptibility factors in mycobacterial infection. Genetics and body morphotype. Infect Dis Clin North Am. 2002;16(1):163-86. [Medline].
Kwon YS, Kim EJ, Lee SH, Suh GY, Chung MP, Kim H, et al. Decreased cytokine production in patients with nontuberculous mycobacterial lung disease. Lung. Dec 2007;185(6):337-41. [Medline].
Levy I, Grisaru-Soen G, Lerner-Geva L, Kerem E, Blau H, Bentur L, et al. Multicenter cross-sectional study of nontuberculous mycobacterial infections among cystic fibrosis patients, Israel. Emerg Infect Dis. Mar 2008;14(3):378-384. [Medline].
Stout JE. Evaluation and management of patients with pulmonary nontuberculous mycobacterial infections. Expert Rev Anti Infect Ther. Dec 2006;4(6):981-93. [Medline].
Erasmus JJ, McAdams HP, Farrell MA. Pulmonary nontuberculous mycobacterial infection. Radiographics. 1999;19(6):1487-505. [Medline].
Patz EF Jr, Swensen SJ, Erasmus J. Pulmonary manifestations of nontuberculous Mycobacterium. Radiol Clin North Am. Jul 1995;33(4):719-29. [Medline].
Davis KK, Kao PN, Jacobs SS, Ruoss SJ. Aerosolized amikacin for treatment of pulmonary Mycobacterium avium infections: an observational case series. BMC Pulm Med. Feb 23 2007;7:2. [Medline].
Further Reading
Keywords
nontuberculosis mycobacterial infection, nontuberculous mycobacterial infection, NTM, tuberculosi s, TB, Mycobacterium avium-intracellulare complex, Mycobacterium kansasii, Mycobacterium xenopi, M avium-intracellulare complex, M kansasii, M xenopi, MAI complex, MAC, Mycobacterium tuberculosis, M tuberculosis, MTB
