Tuberculosis

Question 1

Epidemiology

• Percentage of population that carry M. tuberculosis
• Percentage of those infected that develop disease in their lifetime

Answer 1

• 1/3
• 10%

Question 2

Route of transmission

Answer 2

Inhalation of bacilli in aerosolised droplets from a person with active disease

Question 3

Risk factors for tuberculosis (2 main categories)

Answer 3

1. Living and working conditions

• Infected contacts
• Asian and African countries
• Homelessness, overcrowding
• IV drug use
• Alcoholism

2. Immunocompromise

• HIV
• Smoking
• Silicosis
• Diabetes
• Malnutrition
• Steroids
• Immunosuppressants
• Babies and young children

Question 4

Aetiological organism

• Features of cell wall and the significance of this
• Aerobic / anaerobic
• Intracellular / extracellular
• Staining and shape
• Rate of growth

Answer 4

Mycobacterium tuberculosis

• Mycolic acid creates a thick, waxy, lipid-rich cell wall - resists killing by oxygen free radicals inside phagolysosome
• Aerobic
• Intracellular
• Acid-fast bacillus (red on Ziehl-Neelson stain and resists destaining with acid). Stains weakly positive on gram stain
• Slow-growing

Question 5

Formation of granulomas (5 steps)

Answer 5

• Macrophages secrete IL-12 to activate TH1 cells
• Lymphocytes surround infected macrophages
• Other macrophages fuse with infected macrophage, making a giant multinucleated cell
• Bacilli inside resist immune response
• Abnormal central cell death causes caseous necrosis

Question 6

Symptoms of pulmonary tuberculosis

Answer 6

1. Chronic cough (dry → mucoid → purulent → bloody)
2. Fever, night sweats, chills, weight loss, fatigue
3. Chest pain and dyspnoea

Question 7

Signs of pulmonary tuberculosis

Answer 7

1. Dullness on percussion
2. Decreased fremitus
3. Crackles
4. Clubbing

Question 8

Investigations for tuberculosis

Answer 8

1. CXR

• Focal infiltration, Gohn focus
• Calcification, cavitation, fibrosis, lymph node enlargement

2. Sputum samples

• 3 mornings in a row
• Acid fast, microscopy, culture and sensitivities

Other tests

• Bronchoscopy, pleural tap
• HIV serology
• Mantoux and Quantiferon (latent TB - less useful)

Question 9

Management of active tuberculosis

Answer 9

First 2 months (IPREP)

1. Isoniazid + pyridoxine
2. Rifampicin
3. Ethambutol
4. Pyrazinamide

Next 4 months

1. Isoniazid
2. Rifampicin

Question 10

Extrapulmonary tuberculosis

1. High risk group
2. Organs affected
3. Type of TB caused by haematogenous spread (disseminated)

Answer 10

1. Immunosuppressed persons
2. Almost any organ can be affected
   
   • Pleura (tuberculous pleurisy)
   • Meninges (tuberculous meningitis)
   • Lymph nodes (lymphadenopathy)
   • Urogenital (urogenital tuberculosis)
   • Bone (Pott disease of the spine, osseous tuberculosis - osteomyelitis)
3. Miliary TB
   
   • Millet lesions seen on CXR
   • Accounts for 10% of extrapulmonary cases

Question 11

Drug side effects

• Isoniazid
• Rifampicin
• Ethambutol

Answer 11

• Isoniazid - peripheral neuropathy and hepatitis
• Rifampicin - red tears/urine and hepatitis
• Ethambutol - colour blindness (optic neuritis)