Medically Fit For Exams
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TB (Tuberculosis)

Definition

  • Infection caused by mycobacterium tuberculosis or mycobacterium bovis or mycobacterium africanum

 

Risk Factors

  • Recent travel to, or residence in, an area with high prevalence
    • High risk countries include SE Asia, Africa (especially sub-saharan), middle east, Indonesia
    • Within the UK: London and Birmingham are high risk
  • HIV
  • Immunosuppression
  • Crowded living conditions
  • Old or young age
  • Lung damage

 

Differential diagnoses

  • Pneumonia
  • Cancer
  • Benign tumour/abscess
  • Sarcoidosis
  • Mesothelioma (asbestos)
  • COPD
  • Asthma

 

Epidemiology

  • High risk areas
    • High risk countries include SE Asia, Africa (especially sub-saharan), middle east, Indonesia
    • Within the UK: London and Birmingham are high risk
  • 1/3 of the world is infected (some are latent)
  • Most cases are in Africa, China and India
  • Since 2005 has been slow decline in cases
  • 99% of cases don’t show many symptoms (latent)
  • 10% of latent cases reactivate

 

Aetiology

  • Spread by droplets in the air
  • Usually infects lungs first, may spread
  • It is the immune response to the bacteria that causes the damage: little damage in latent because no/mild immune response

 

Clinical features

  • Productive cough, haemoptysis
  • Night sweats
  • Weight loss
  • Anorexia
  • Clubbing
  • Cough and hoarse voice if laryngeal involvement
  • If lymph node involvement
    • Supraclavicular and cervical
    • Firm non-tender
  • Can spread to GI system bone and spine

 

Pathophysiology

  • Type 4 hypersensitivity
  • Bacteria engulfed by macrophages, but not killed, because has waxy cell wall
  • MHC2 presentation, T cell activation
  • Forms Ghon focus
  • Inflammatory cells, cytokine mediated
  • Fibrin laid down
  • Causes caseating granulomas

 

Investigations

  • CXR – military, consolidation (usually upper lobe), cavitating lesions, calcified ghon focus, pleural effusion
  • Mantoux test - >15mm (10 if high risk, 5 if HIV+)
  • Quantiferon-TB blood test – measures IFN-g levels
  • Sputum – 3 samples, can culture and check for bacteria

 

Management

  • DOTS (Directly observed therapy short-course)
    • Introduced by WHO in 1995
    • Political and financial commitment
    • Case detection through quality-assured bacteriology
    • Standardized treatment, with supervision and patient support
    • An effective drug supply and management system (free)
    • Monitoring and evaluation system, and impact measurement
  • Drug regime:
    • 4 antibiotic drugs:
      • Rifampicin – 6 months
      • Isoniazid – 6 months
      • Pyrazinamide – 2 months
      • Ethambutol or Streptomycin – 2 months
    • Extrapulmonary TB – antibiotics for 12 months, plus steroid (prednisolone)
    • Latent TB – may not require treatment, rifampicin + isoniazid for 3 months

 

Prognosis

  • 50% mortality for untreated active disease
  • Very high mortality for miliary (TB in blood)
  • Treatment is effective if followed
TB.docx
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