TB

Question 1

TB - overview

Answer 1

1. Caused by Mycobacterium tuberculosis
2. TB infection more likely to progress to disease in infants and young children, compared with adults
3. Transmission by droplet infection (respiratory route)
4. Once inhaled, some bacilli remain at the site of entry and the rest are carried to regional lymph nodes
5. The bacilli multiply at both sites. Organisms can then spread via blood and lymphatics

Question 2

TB - clinical features

Answer 2

1. Primary infection (may be asymptomatic or symptomatic)
2. If asymptomatic - a local inflammatory reaction has limited the progression of infection, but the disease remains latent. If symptomatic, the local host response has failed to contain the inhaled tubercle bacilli, leading to (5):
   - Fever
   - Anorexia
   - Weight loss
   - Malaise
   - Cough
   Note - although primary infection commonly occurs in the lungs, it may also involve other organs including gut, skin and superficial lymph nodes
3. Dormancy and dissemination - both asymptomatic and symptomatic infections may become dormant but subsequently reactivate and spread by lymphohaematological routes
4. Reactivation
5. Post-primary TB - may present as local disease or may be widely disseminated, miliary TB (sites of dissemination include bone, joints, kidneys, pericardium and CNS); in infants and young children, seeding of the CNS is particularly likely, causing tuberculous meningitis

Question 3

TB - ix/dx

Answer 3

Dx often made with triad:

1. Recent close contact with infectious case
2. Positive tuberculin skin test (TST, same as Mantoux test) or interferon-gamma release assay (IGRA)
   - Note: positive TST may be due to latent infection, active infection or past BCG vaccination
   - Positive IGRA tests indicate TB infectoin rather than BCG vaccination
   - If co-infection with HIV, dx more difficult because both TST and IGRA are unreactive with advanced immune suppression
3. Suggestive findings on CXR and physical examination

Other ix

4. Gastric washings on three consecutive mornings (rather than sputum samples because these are usually swallowed by children) to visualise or culture acid-fast bacilli
5. HIV testing PLUS UEC, lymph node excision, CSF and radiological examinations where appropriate

Question 4

TB - mx

Answer 4

1. Rifampicin (600mg if >50kg, 450mg if >14y but 14y, 10mg/kg up to 300mg if 14y, 35mg/kg up to 2g if 14y, 20mg/kg up to 1200mg if