Tuberculosis

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Referral

Definition

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB) but can involve other organs (extrapulmonary TB).

Aetiology

TB is caused by the bacterium Mycobacterium tuberculosis. Transmission occurs through airborne droplets from infected individuals with active pulmonary TB.

Pathophysiology

TB develops in the following stages:

  • Primary infection: inhaled bacteria reach the alveoli, where they are engulfed by macrophages. In most individuals, the immune system contains the infection, forming granulomas.
  • Latent TB: the bacteria remain dormant within granulomas, causing no symptoms but persisting for years.
  • Active TB: reactivation occurs when the immune system is weakened, allowing bacteria to multiply and spread.

Risk factors

  • Close contact with individuals with active TB.
  • Immunosuppression (e.g., HIV, chemotherapy, corticosteroids).
  • Malnutrition or poor socioeconomic conditions.
  • Living in or travelling to endemic areas.
  • Chronic conditions such as diabetes or chronic kidney disease.

Signs and symptoms

1. Pulmonary TB:

  • Persistent cough lasting more than 3 weeks.
  • Haemoptysis (coughing up blood).
  • Chest pain.
  • Fatigue, fever, and night sweats.
  • Unintentional weight loss.

2. Extrapulmonary TB:

  • Depends on the site of infection:
    • Lymph nodes: painless swelling, often in the neck (scrofula).
    • Bone/joints: pain and swelling (e.g., Pott’s disease in the spine).
    • CNS: headache, confusion, or meningitis symptoms.
    • Genitourinary: dysuria, haematuria, or pelvic pain.

Investigations

  • Chest X-ray:
    • Active TB: consolidation, cavitation, or hilar lymphadenopathy.
    • Healed TB: fibrosis, calcifications, or pleural thickening.
  • Sputum microscopy and culture: Acid-fast bacilli (AFB) seen on Ziehl-Neelsen stain confirm TB. Culture is more sensitive but takes longer.
  • Interferon-gamma release assays (IGRA): used to detect latent TB in individuals with prior BCG vaccination.
  • Tuberculin skin test (Mantoux test): indicates TB exposure but cannot distinguish between latent and active TB.
  • CT scan: for detailed evaluation of pulmonary or extrapulmonary TB.
  • Biopsy: for extrapulmonary TB, showing caseating granulomas.

Management

1. Latent TB:

  • 6 months of isoniazid with pyridoxine (to prevent peripheral neuropathy).
  • Alternative: 3 months of isoniazid and rifampicin.

2. Active TB:

Treatment involves a 6-month regimen of antibiotics:

  • Intensive phase (first 2 months): isoniazid, rifampicin, pyrazinamide, and ethambutol (HRZE).
  • Continuation phase (next 4 months): isoniazid and rifampicin.

3. Drug-resistant TB:

  • Consult with a TB specialist for second-line treatment options, which may include fluoroquinolones or bedaquiline.

4. Supportive management:

  • Provide nutritional support.
  • Ensure adherence to treatment to prevent resistance.

Referral

Refer to secondary care in the following scenarios:

  • Respiratory Specialist: for confirmation of diagnosis and initiation of treatment for active or latent TB.
  • Infectious Disease Specialist: for extrapulmonary TB or suspected drug-resistant TB.
  • Hospital admission:
    • Severe respiratory symptoms or haemoptysis.
    • Significant systemic symptoms (e.g., fever, weight loss) requiring inpatient care.
 
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