Tuberculosis (summary)

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This is a basic article for medical students and other non-radiologists

Tuberculosis (TB) is a non-bacterial multisystem infection that often affects the lungs. It may be a primary tuberculous infection, secondary infection or appear as chronic scarring. TB may also be seen on a chest x-ray as lymphadenopathy.

Reference article

This is a summary article; read more in our article on tuberculosis.

Summary

  • epidemiology
    • developing nations - adolescents and young adults
    • developed nations - immigrants, homeless and HIV-infected
  • presentation
    • ​primary infection
      • usually asymptomatic
      • may feel generally unwell or have a small pleural effusion
    • post-primary infection
      • when patients usually present to clinicians
      • systemic symptoms
        • malaise
        • weight loss
        • fever
        • night sweats
      • pulmonary symptoms
        • productive cough (mucopurulent or blood-stained)
        • shortness of breath
        • chest pain
      • extrapulmonary symptoms
        • variable on location of lesions
  • pathology
    • M. tuberculosis
      • aerobic mycobacterium
      • Gram staining ineffective due to waxy coating
    • primary infection
      • non-immune host exposed to M. tuberculosis
      • primary lesion usually occurs in the upper region of the lung
        • Ghon focus describes the initial granulomatous lesion 
      • Ghon complex is the calcified focus with associated mediastinal lymphadenopathy
      • most primary infections result in healing
        • leads to post-primary immunity and latent infection
    • post-primary infection (secondary tuberculosis)
      • harbored bacteria is reactivated after primary infection
        • occurs in immunocompromised individuals (e.g. HIV, steroid therapy, cytotoxic drugs)
      • lung infection causes patchy consolidation or cavitation
      • extrapulmonary infection may involve meninges, bones, lymph nodes, urinary tract or GI tract
    • miliary tuberculosis
      • disseminated disease from TB infection in immunocompromised patients
        • may follow primary or post-primary infection
      • poor prognosis
  • investigation
    • chest x-ray
    • sputum sample
      • Ziehl-Neelsen stain for acid-fast bacilli
      • culture for confirmation of diagnosis and sensitivity testing
    • HIV serology
    • lumbar puncture
      • investigation for TB meningitis 
    • blood tests
  • treatment
    • active TB
      • 4-drug regimen of rifampin, isoniazid, pyrazinamide and ethambutol (2 months)
      • continuation of rifampin and isoniazid (4 months)
    • latent TB
      • rifampin and isoniazid (3 months)
      • OR isoniazid alone (6 months)
    • consideration of multidrug-resistant TB
  • screening and prevention
    • Mantoux test (tuberculin skin test)
      • screening for latent tuberculosis
    • BCG vaccine
      • recommended for high-risk groups

Radiographic features

Chest radiograph
CT chest

As with most chest pathology, CT shows the same findings as demonstrated on the chest radiograph, but with more detail and clarify. Smaller nodules can be seen. Lymph nodes can be assessed in more detail.

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