Tuberculosis

Question 1

Describe the epidemiology of TB

Answer 1

30% of the world’s population have latent TB

2 billion deaths from TB each year

Highest incidence in central and southern africa

Question 2

Describe the aetiology of TB

Answer 2

Caused by mycobacterium tuberculosis

Gram stain -ve but similar structure to gram stain +ve.

Unique impermeable cell wall

Transmission predominantly from aerosolised droplets or fomites.

Question 3

Where is latent TB often contained in the body?

Answer 3

Hilar lymph nodes and Ghon focus

Question 4

Describe the histopathology of TB

Answer 4

Granulomatous inflammation with caseous necrosis

Question 5

List the host risk factors for TB

Answer 5

Extremes of age

Stress and starvation

Immunocompromised host:

• HIV
• Alcoholism
• Steroids and immunosuppressants
• Anti TNF treatment for autoimmune diseases

Other risk factors:

• Malignancy
• Renal failure
• Diabetes mellitus
• Vitamin D deficiency

Question 6

Name some clinical features of TB

Answer 6

Varies according to site of infection; insidious onset.

Systemic features:

• Fevers
• Night sweats
• Weight loss

Pulmonary:

• Cough
• Sputum
• Haemoptysis
• Dyspnoea

Lymph nodes = typically cervical & axillary (may become necrotic)

Other sites = local symptoms of inflammation & tissue necrosis

Question 7

List investigations for TB

Answer 7

• Full blood count (FBC) : possible leukocytosis (↑ WCC)
• Urea & electrolytes (U&Es) : usually normal
• Liver function tests (LFTs) : possibly raised
• C-reactive protein (CRP) : mild-moderate rise only
• Lactate : usually normal (no sepsis)
• Chest radiograph (CXR) : upper lobe cavitating pneumonia
  
  • Miliary shadowing
  • Hilar lymphadenopathy
  • Pleural effusion
  • Pericardial effusion

CT/MR scans : thorax / abdomen / spine / bones / head

Laparoscopy / Thoracoscopy : direct visualisation & biopsy

Other biopsies : lymph nodes / bones / cold abscesses

Question 8

What does this x-ray show?

Answer 8

Left upper lobe tuberculosis

Question 9

What does this x-ray show?

Answer 9

Miliary TB (TB infection was never contained in ghon focus, spread throughout body tissues)

Question 10

What does this x-ray show?

Answer 10

Pericardial effusion caused by TB.

Large due to slow growing TB

Question 11

Which microbiological investigations can be conducted to confirm TB?

Answer 11

Sputum:

• Ziehl-Neelsen stain → Acid-Fast Bacilli (AFBs) = pink
• Auramine-Phenol stain → AFBs = fluorescent

Sputum, pleural fluid, pericardial fluid, blood, urine, CSF & biopsies→ culture (on Löwenstein–Jensen or liquid medium) & sensitivities

Question 12

How is TB treated?

Answer 12

Multi-drug treatment required to prevent resistance

• Rifampicin for 6 months
• Isoniazid for 6 months
• Pyrazinamide for 2 months
• Ethambutol for 2 months

(TB in the CNS requires 12 months of treatment)

Pyridoxine to prevent neuropathy from isoniazid

Steroids if CNS or pericardial infection

Vitamin D if deficient

Question 13

What can be given to prevent TB?

Answer 13

Prevention of primary infection :

For active TB cases :

• Respiratory isolation
• Prompt diagnosis & treatment
• Contact tracing & testing

Vaccination with Bacillus Calmette–Guérin (BCG) :

• ~25% prevention of primary infection
• ~70% prevention of active infection

Question 14

How is latent TB screened for?

What is the treatment of latent TB?

Answer 14

Prevention of re-activation :

• Screening for latent TB infection & treatment :
  
  • Tuberculin skins tests (TST)
  • TB interferon-gamma release assays (IGRA)

Treatment for latent TB :

• Rifampicin & isoniazid for 3 months