17 Tuberculosis

Question 1

What bacteria causes tuberculosis?

Answer 1

Mycobacterium tuberculosis

Question 2

TB bacili are aerobic, acid and alcohol fast bacili. How are they stained and cultured? How long does it take?

Ie what method and what medium

Answer 2

Stained: Ziehl-Nielsen method

Culture: Lowenstein-Jensen medium

How long?: 2-6 weeks to culture

Question 3

How is TB transmitted? (ie in what form are the TB)

Answer 3

Infected droplets

Question 4

A patient with pulmonary TB must be on anti-TB chemotherapy for 6 months. How long after commencing treatment is their sputum no longer infective?

Answer 4

2 weeks- infectivity of sputum= minimal

Question 5

Who is particularly at risk of acquiring TB in the UK?

Answer 5

• Non-UK born/recent migrants
• Immunocompromised
  
  • Eg HIV, chemo
• Homeless
• Drug users, prisoners

(TB requires prolonged contact- likely to be someone you live with etc)

Question 6

How is a patient tested for a latent TB infection? (2) Explain how they work.

Answer 6

Question 7

What % of people infected with TB will develop primary TB and what % will develop post primary TB?

Answer 7

(post primary- up to 60 yrs post initial infection)

Question 8

Where (in the lungs) is post primary TB most often seen and why?

Answer 8

Upper lobes

Higher pO₂ favoured by Mycobacteria

Question 9

How does latent TB develop into active TB? (5)

Answer 9

1. Cavity formation:
   
   1. ​softening and liquefaction of caseous material- discharged into bronchus
   2. fibrous tissue forms around cavity BUT unable to limit extension of tuberculous process
2. Haemorrhage:
   
   1. Caseous process extends into vessel walls
      
      1. HAEMOPTYSIS
3. Spread to involve rest of lung:
   
   1. Caseous and liquefied material- spread infection through bronchial tree
4. Pleural effusion:
   
   1. TB bacili enter pleura/hypersensitivity reaction
5. Miliary TB:
   
   1. Rupture of caseous pulmonary focus into blood vessel- widespread dissemination of bacili

Question 10

What sites might be involved in extra pulmonary TB?

Answer 10

Lymph nodes, bones, joints, CNS, GI tract, urinary tract

Question 11

How might a patient with TB present clinically?

Answer 11

Gradual onset (weeks/months)

Symptoms:

• Tiredness
• Malaise
• Weight loss
• Fever
• Sweats
• Cough
  
  • Dry/productive (w./ mucoid sputum)
  • Haemoptysis

Signs:

• Crackles (maybe)

Question 12

What may be seen on a chest x-ray for a patient with TB?

Answer 12

• Caviated solid lesions
• Streaky fibrosis
• Flecks of calcification

Question 13

How is TB treated? (RIPE)

Answer 13

COMBINATION OF 4 ANTIBIOTICS - several months

1. Rifampicin
2. Isoniazid (INAH) + (vitamin B6)
3. Pyrazynamide
4. Ethambutol

• all 4- for 2 months*
• rifampicin and isoniazid- for 4 months*

Question 14

Why is vitamin B6 given with INAH (isoniazid)?

Answer 14

To prevent preripheral nerve damage

Question 15

Why are 4 drugs used to treat TB?

Answer 15

Single drugs would allow selection of resistant strains

Unlilely that strains= resistant to all 4 drugs

Question 16

Outline the pathophysiology of TB:

Answer 16