Nontuberculous mycobacterial lung disease
Nontuberculous mycobacterial (NTM) lung disease is chronic pulmonary infection with environmental mycobacteria other than the tuberculosis complex, most often Mycobacterium avium complex (MAC). Diagnosis requires clinical, radiologic, and microbiologic criteria together, not culture positivity alone. First-line therapy for MAC is a macrolide plus a rifamycin plus ethambutol, continued until cultures are negative for 12 months.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
Nontuberculous mycobacteria (NTM) are environmental mycobacterial species other than the Mycobacterium tuberculosis complex and Mycobacterium leprae.
- Epidemiology
MAC is the most common cause of pulmonary NTM infection in the United States, followed by M.
- Risk factors
Structural lung disease: bronchiectasis, chronic obstructive pulmonary disease (COPD), prior tuberculosis, and cystic fibrosis (CF) impair mucociliary clearance and favor colonization.
- Pathophysiology
NTM are slow- or rapid-growing acid-fast organisms recovered from water, soil, and domestic water systems.
- Clinical features
Chronic respiratory symptoms: productive cough over months to years, fatigue, and gradually progressive dyspnea rather than acute onset.
- Differential diagnosis
Pulmonary tuberculosis: a similar fibrocavitary picture, but culture grows M.
- Diagnosis
What establishes the diagnosis: confirmed only when the ATS/IDSA clinical, radiologic, and microbiologic criteria above are all met together; species-level identification is mandatory since susceptibility differs among species.
- Management
First-line, confirm criteria before treating: start therapy only once full ATS/IDSA criteria are met; mild, stable nodular bronchiectatic disease without cavitation can be observed with serial imaging and cultures instead.
- Complications
Progressive bronchiectasis and cavitary destruction: repeated infection cycles worsen airway damage over years.
- Prognosis
Nodular bronchiectatic MAC disease typically follows an indolent, waxing and waning course over years, but relapse and reinfection with a distinct strain are common even after successful therapy.
- Prevention
Primary MAC prophylaxis in HIV infection: azithromycin 1200 mg PO once weekly (or 600 mg PO twice weekly), or clarithromycin 500 mg PO twice daily, was formerly recommended below a CD4 count of…
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.
Related articles
- Bronchiectasis
Bronchiectasis is chronic, irreversible bronchial dilation from a cycle of infection, inflammation, and airway destruction, diagnosed by high-resolution CT and managed with airway clearance, treatment of the underlying cause, and antibiotics for exacerbations.
- Chronic obstructive pulmonary disease (COPD)
Chronic obstructive pulmonary disease is a persistent, usually progressive airflow obstruction driven mainly by cigarette smoke, confirmed by a postbronchodilator FEV1/forced vital capacity (FVC) ratio below 0.70 and staged by GOLD spirometric grade plus symptom/exacerbation group. Maintenance management is a stepwise ladder of smoking cessation, long-acting bronchodilators, add-on inhaled glucocorticoid, roflumilast, or azithromycin for frequent exacerbators, long-term oxygen for resting hypoxemia, and vaccination, with acute exacerbations managed as a separate protocol.
- Cystic fibrosis
Cystic fibrosis is an autosomal recessive CFTR chloride-channel disorder causing thick secretions, bronchiectasis, and exocrine pancreatic insufficiency, diagnosed by elevated sweat chloride confirmed with CFTR genotyping and managed with CFTR modulators, airway clearance, and pancreatic enzyme replacement.
- Tuberculosis
Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.
- HIV antiretroviral therapy (ART)
Antiretroviral therapy (ART) combines three or more drugs from at least two classes to suppress HIV replication. First-line therapy is bictegravir/emtricitabine/tenofovir alafenamide or dolutegravir-based triple therapy, started as soon as the patient is ready regardless of CD4 count, and continued for life to prevent AIDS and transmission.
- Pneumocystis jirovecii pneumonia
Pneumocystis jirovecii pneumonia is a subacute, often hypoxic pneumonia in patients with CD4 counts below 200/mcL or comparable immunosuppression, diagnosed by organism visualization on induced sputum or bronchoalveolar lavage and treated with 21 days of high-dose trimethoprim-sulfamethoxazole plus adjunctive steroids when hypoxic.
- Hypersensitivity pneumonitis
Hypersensitivity pneumonitis is a mixed type III/IV immune reaction to repeated inhalation of an organic antigen in a sensitized host, producing noncaseating granulomas and bronchiolocentric inflammation. Removal of the offending antigen is the essential first step in treatment; glucocorticoids are added for significant hypoxemia or symptom burden, and unremitting exposure can progress to fibrotic lung disease indistinguishable from idiopathic pulmonary fibrosis.