Mycobacterial Pulmonary Diseases, Nontuberculous

Key Features

Essentials of Diagnosis

• Chronic cough, sputum production, and fatigue

• Less commonly, malaise, dyspnea, fever, hemoptysis, and weight loss

• Parenchymal opacities on chest radiograph, most often with thin-walled cavities or multiple small nodules associated with bronchiectasis

• Isolation of nontuberculous mycobacteria in a sputum culture

General Considerations

• Nontuberculous mycobacteria (NTM) or atypical mycobacteria are ubiquitous in water and soil

• NTM may colonize the airways or appear in cultures due to environmental contamination

• Organisms are not communicable from person to person

• NTM are often resistant to most antituberculous drugs

• Complementary data are important for diagnosis, as NTM can reside or colonize airways without causing clinical disease

• Mycobacterium avium complex (MAC) is the most common cause of NTM pulmonary disease in the United States

• Mycobacterium kansasii is the second most common pulmonary pathogen

• Other NTM that can cause pulmonary disease include

  • Mycobacterium abscessus

  • Mycobacterium xenopi

  • Mycobacterium malmoense

• Most organisms cause a chronic progressive pulmonary infection similar to tuberculosis but more slowly progressive

• Many patients have AIDS or preexisting lung disease

• Disseminated disease is rare in immunocompetent patients

• Disseminated MAC infection is common in patients with AIDS

Clinical Findings

Symptoms and Signs

• Chronic cough, sputum production, and fatigue

• Malaise, dyspnea, fever, hemoptysis, and weight loss are less common

• Symptoms from coexisting lung disease can confound the evaluation

• New or worsening infiltrates, adenopathy, or pleural effusion are described in HIV-positive patients with NTM infection as part of the immune reconstitution inflammatory syndrome following institution of antiretroviral therapy

Differential Diagnosis

• Postviral

• Bronchitis, especially in smokers

• Bronchiectasis

• Tuberculosis

• Cystic fibrosis

• Pertussis

• Mycoplasma

• Chlamydia

• Respiratory syncytial virus

Diagnosis

Laboratory Tests

• Diagnosis rests on recovery of the pathogen from cultures

• Bronchial washings are considered more sensitive than expectorated sputum, but their specificity for clinical disease is unknown

• Bacteriologic diagnostic criteria in immunocompetent persons include

  • Positive culture results from at least two separate expectorated sputum samples; or

  • Positive culture from at least one bronchial wash; or

  • Positive culture from pleural fluid or any other normally sterile site

• Criteria for infection in HIV-positive patients is less stringent

• DNA probes or high-pressure liquid chromatography allow rapid species identification of NTM

• Drug susceptibility testing is recommended only as follows:

  • M kansasii and rifampin

  • Rapid growers (Mycobacterium fortuitum, M abscessus, and M chelonae) and amikacin, doxycycline, imipenem, fluoroquinolones, clarithromycin, cefoxitin, and sulfonamides

Imaging Studies

• Chest radiograph with progressive or persistent opacities for 2 months, cavitary lesions, and multiple nodular densities

• Cavities are usually thin walled and with less surrounding opacity than seen in M tuberculosis

• High-resolution CT scan may show multiple small ...