Skip to Main Content

Key Features

Essentials of Diagnosis

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

  • Pulmonary infiltrates on chest radiograph, most often apical

  • Positive tuberculin skin test reaction (most cases)

  • Smear of sputum positive for acid-fast bacilli or culture of sputum positive for Mycobacterium tuberculosis (MTB)

General Considerations

  • Latent tuberculosis infection (LTBI) occurs when bacilli are contained within granulomata, the typical response to infection in immunocompetent persons

    • Nontransmissible, but may become active disease if a person's immune function becomes impaired

    • Reactivation occurs within 2 years in up to 50% of HIV-positive patients

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

  • Resistance may be to single or multiple drugs

    • Drug-resistant TB is resistant to one first-line antituberculous drug, either isoniazid or rifampin

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

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

Demographics

  • HIV increases the risk of reactivation tuberculosis

  • Risk factors for drug resistance include

    • Immigration from a region with drug-resistant tuberculosis

    • Close contact with a patient infected with drug-resistant tuberculosis

    • Unsuccessful prior therapy

    • Patient noncompliance

Clinical Findings

Symptoms and Signs

  • Cough is most common

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

  • Slowly progressive constitutional symptoms

    • Malaise

    • Anorexia

    • Weight loss

    • Fever

    • Night sweats

  • Patients appear chronically ill and malnourished

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

  • Extrapulmonary disease is especially common, often with lymphadenitis or miliary disease

  • Atypical presentations are common

Differential Diagnosis

  • Pneumonia or lung abscess

  • Lung cancer

  • Lymphoma

  • Mycobacterium avium complex (or other nontuberculous mycobacteria)

  • Sarcoidosis

  • Fungal infection, eg, histoplasmosis

  • Endocarditis

  • Nocardiosis

Diagnosis

Laboratory Tests

  • Tuberculin skin test (TST)

    • The Mantoux test is the preferred method: 0.1 mL of purified protein derivative (PPD) containing 5 tuberculin units is injected intradermally on the volar surface of the forearm using a 27-gauge needle on a tuberculin syringe. After 48–72 hours, the transverse width in millimeters of induration at the skin test site is measured

    • Table 9–13 summarizes the criteria established by the Centers for Disease Control and Prevention (CDC) for interpretation of the Mantoux TST

  • Interferon gamma release assays (IGRAs) (including the QuantiFERON and T-SPOT tests) are in vitro assays of CD4+ T-cell-mediated interferon gamma release in response to stimulation by specific M tuberculosis antigens

    • In endemic areas, IGRAs are no more sensitive than the TST in active tuberculosis (20–40% false-negative rate) and cannot distinguish active from latent disease

    • IGRAs should not be used to exclude active tuberculosis

Table 9–13.Classification of positive tuberculin skin test reactions.1

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.