Tuberculosis, Pulmonary

Key Features

Essentials of Diagnosis

• Fatigue, weight loss, fever, night sweats, and productive cough

• Risk factors for acquisition of infection: household exposure, incarceration, drug use, travel to an endemic area

• Chest radiograph: pulmonary opacities, most often apical

• Sputum smear positive for acid-fast bacilli or sputum culture positive for Mycobacterium tuberculosis

General Considerations

• Primary infection

  • Occurs with inhalation of airborne droplets containing viable tubercle bacilli and subsequent lymphangitic and hematogenous spread before immunity develops

  • Up to one-third of new urban cases are from primary infection acquired by person-to-person transmission

• Latent tuberculosis infection (LTBI)

  • Occurs when bacilli are contained within granulomata

  • Nontransmissible while latent, but may become active disease if the infected person's immune function becomes impaired

• Drug-resistant strains of M tuberculosis are increasingly common worldwide, though rates in the US have fallen to less than 1.3%

• Risk factors for drug resistance include

  • Immigration from countries with a high prevalence of drug-resistant tuberculosis

  • Close and prolonged contact with individuals with drug-resistant tuberculosis

  • Unsuccessful previous antituberculosis therapy

  • Patient nonadherence to such therapy

• Resistance may be to single or multiple drugs

  • Drug-resistant tuberculosis is resistant to one first-line antituberculous drug, either isoniazid (INH) or rifampin (RIF)

  • Multidrug-resistant tuberculosis (MDR-TB) is resistant to INH and RIF, and possibly additional agents

  • Extensively drug-resistant tuberculosis (XDR-TB) is resistant to INH, RIF, fluoroquinolones and either aminoglycosides or capreomycin or both

• Nonadherence is a major cause of treatment failure, disease transmission, and development of drug resistance

Demographics

• Infects one-third of the world's population

• In 2014, there were 9.6 million new cases of tuberculosis worldwide with 1.5 million people dying of the disease

• In the United States, an estimated that 11 million people are infected with M tuberculosis and in 2014 there were 9421 active cases

• Occurs disproportionately among malnourished, homeless, and marginally housed individuals

• Risk factors for reactivation

  • Gastrectomy

  • Silicosis

  • Diabetes mellitus

  • HIV

  • Immunosuppressive drugs

• Risk factors for drug resistance

  • Immigration from regions with drug-resistant tuberculosis

  • Close contact with patients infected with drug-resistant tuberculosis

  • Unsuccessful prior antituberculosis therapy

  • Patient noncompliance with such treatment

Clinical Findings

Symptoms and Signs

• Cough is the most common symptom

• Blood-streaked sputum is common, frank hemoptysis is rare

• Slowly progressive constitutional symptoms include malaise, anorexia, weight loss, fever, and night sweats

• Patients appear chronically ill

• Chest examination is nonspecific; post-tussive apical rales are classic

• Atypical presentations are becoming more common, usually among the elderly and HIV-positive patients

Differential Diagnosis

• Pneumonia

• Lung abscess

• Lung cancer or lymphoma

• Mycobacterium avium complex (or other nontuberculous mycobacterial infection)

• Sarcoidosis

• Fungal infection, eg, histoplasmosis

• Endocarditis

• Silicosis or asbestosis

• Nocardiosis

Diagnosis

Laboratory Tests

• Tuberculin skin test...