Tuberculosis

Chronic disease caused by Mycobacterium tuberculosis (generally)

Aetiology

  • M. tb is the main causative organism in humans – rod-shaped gram-positive bacillus, acid fast
  • M. bovis can jump the species barrier from cattle to humans

Risk factors

  • Immigrants
  • Recent contacts
  • Social deprivation
  • Immunosuppression - virulent MTB or atypical infection

Pathophysiology

  • Type IV hypersensitivity - granulomas with necrosis
 
  1. Pathogen transmitted via aerosol route and reaches alveoli
  1. Pathogen phagocytosed in alveoli and carried to hilar lymph nodes → immune activation
  1. This leads to a granulomatous response in the nodes, with caseous necrosis occurring in the granulomas
  1. The infection is either cleared completely or will become latent (LTBI)
  1. In a few cases the infection is overwhelming and spreads throughout the body, setting up many foci of infection (e.g. miliary TB) - extra-pulmonary TB

Clinical presentation

Pulmonary features

  • 90% present with pulmonary features only
  • Cough +/- haemoptysis
  • Dyspnoea

Extrapulmonary features (10%)

  • Fever and chills
  • Night sweats
  • Fatigue
  • Loss of appetite
  • Weight loss
  • Erythema nodosum
  • Range of other organ-specific symptoms

Investigations

Active TB

  • CXR
    • Shadows, lesions, consolidation
    • Ghon focus in periphery of mid zone of lung - primary site of infection
    • Bilateral hilar lymphadenopathy
    • ‘Miliary shadowing’ = miliary TB
  • Samples e.g. sputum, pus, or a tissue biopsy
    • 3 separate sputum samples in pulmonary TB (including one early morning sample)
    • Can do broncoscopy and lavage or gastric washings (rarely required)
    • Ziehl-Neelson stain - tests for AFB, rapid (24h)
    • Histology - granuloma with central caseous necrosis

Latent TB

  • Tuberculin skin test

Management

Active TB

  • Rifampicin, Isoniazid, Pyrazinamide and Ethambutol for 4 months
  • Rifampicin and Isoniazid for a further 2 months

Latent TB

  • Rifampicin and Isoniazid for 3 months
  • OR Isoniazid for 6 months
  • SGOT/SGPT three fold with nausea and vomiting
  • SGOT/SGPT five fold
  • Icterus whole body