Tuberculosis (summary)

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
    • ​extrapulmonaryextrapulmonary 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)
    • harboured 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
• radiographic features (CT & CXR)
  • primary infection
    • parenchymal consolidation
    • lymphadenopathy
    • pleural effusion
    • Ghon complex
  • post-primary infection
    • patchy consolidation (upper zones)
    • cavitation
    • healing results in fibrosis
    • pleural disease
  • miliary tuberculosis
    • 1-3 mm diameter miliary nodules
    • uniform size and distribution throughout both lungs
  • extrapulmonary tuberculosis
    • tuberculoma within an affected organ
    • widely variable
• treatment
  • active TB
    • 4-drug regimen of rifampicin, isoniazid, pyrazinamide and ethambutol (2 months)
    • continuation of rifampicin and isoniazid (4 months)
  • latent TB
    • rifampicin 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