TB

Question 1

What pathogen causes TB?

Answer 1

Mycobacterium Tuberculosis

Question 2

How would you describe the pathogen that causes TB?

Answer 2

Acid fast bacilli

Stains Bright Red with Ziehl-Neelsen stain

Question 3

How is TB contracted?

How does it spread?

Answer 3

by inhaling saliva droplets

via blood and lymph nodes

Question 4

What is a Ghon Focus?

What is a Ghon Complex?

what does this lead to?

Answer 4

Lesion in the lungs, contains macrophages

macrophages frequently spread to regional lymph nodes
lung lesion + affected lymph node = Ghon Complex

leads to formation of a granuloma (containing the bacteria) to develop around the body. Granulomas have caseous necrosis at the centre.

Question 5

Which inflammatory response mediates TB

Answer 5

Type 4 hypersensitivity

Question 6

What is active TB

How does the initial lesion heal in healthy individuals

Answer 6

Active infection in various areas of the body

in majority of cases body is able to kill and clear infection

In healthy individuals, heals by fibrosis

Question 7

What is latent TB?

What is Secondary TB?

Answer 7

Immune system may encapsulate sites of infection and stop the progression of disease

when latent TB reactivates (usually in the immunpcompromised)

Question 8

Where does secondary (post-primary) TB develop?

Answer 8

generally in the apex of the lung

may spread locally or to more distant sites

Question 9

What is disseminated TB

Answer 9

when the immune system is unable to control the infection

severe disease is called Milliary TB

Question 10

What are causes of immunocompromise ?

Answer 10

• immunosuppresive drugs including steroids
• HIV
• malnutrition

Question 11

Where may extra-pulmonary infection occur?

Answer 11

1. lymph nodes (cold abcess)
2. pleura
3. pericardium
4. CNS
5. gastrointestinal system
6. GU system
7. bones and joints
8. cutaneous TB affecting skin

Question 12

How does TB present?

Answer 12

1. Lethargy
2. Fever +/- night sweats
3. cough +/- haemoptysis
4. weight loss
5. lympadenopathy
6. erythema nodosum
7. spinal pain in spinal TB - potts disease of the spine

Question 13

What does the BCG vaccine contain

Answer 13

live, attenuated mycobacterium bovis

Question 14

What is the BCG vaccine good at protecting against?

Answer 14

severe and complicated TB

less effective at protecting against pulmonary TB

Question 15

What must you do prior to BCG vaccination?

Answer 15

Do a Mantoux test

give vaccine only if this test is negative

Question 16

Who should be given a BCG vaccine?

Answer 16

1. Neonates born in areas of the UK with high rates of TB
2. Neonates with relatives from countries with a high rate of TB
3. Neonates with a family history of TB
4. Unvaccinated older children and young adults (< 35) who have close contact with TB
5. Unvaccinated children or young adults that recently arrived from a country with a high rate of TB
6. Healthcare workers

Question 17

What are contraindications to BCG vaccine?

Answer 17

1. previous BCG vaccine
2. previous TB
3. positive tuberculin test
4. HIV
5. pregnancy

Question 18

What investigations can you do for Latent TB? drawbacks?

Answer 18

Mantoux test

Interferon Gamma release assay

Question 19

How does the Mantoux test work

When is it considered positive?

What must you then do?

Answer 19

will be positive in cases of previous exposure e.g BCG vaccine or latent TB

if induration and erythema > 10mm = positive result

if strongly positive TB is likely. response to BCG decreases over time

Need to do further Ix e.g Chest Xray

Question 20

How does IGRA work

Answer 20

blood test

looks for latent TB

used for confirmation if positive mantoux or had a previous BCG

Question 21

How do you diagnose active TB? Which is gold standard?

Answer 21

1. CXR
2. Sputum smear - stained for zeihl-neelsen
3. Sputum culture gold standard
4. Nucleic Acid Amplification Test (NAAT)

Question 22

What is the classical finding on CXR in TB

Answer 22

upper lobe cavitation (usually not primary)

bilateral hilar lympadenopathy

Question 23

What is the added benefit of sputum culture in TB?

how many samples are needed?

Answer 23

can assess drug sensitivties

3 samples need to be tested

Question 24

How do you manage latent TB?

Answer 24

Isoniazid and Rifampicin for 3 months

or

Isoniazid for 6 months

Question 25

How do you manage active TB?

How long for each?

Answer 25

Rifampicin (6 months)
Isoniazid (+ pyridoxine) (6months)
Pyrazinamide (2 months)
Ethambutol (2 months)

Question 26

what must you give alongside isoniazid? why?

Answer 26

Pyridoxine (vitamin B6)

prophylaxis for the peripheral neuropathy isoniazid can cause

Question 27

What are the side effects of each of the drugs?

What are RIP associated with?

Answer 27

Rifampicin - orange/red discolouration of secretions (tears/urine). also induces cytochrome P450 enzymes - effects metabolism of drugs using this e.g Contraceptives

Isoniazid - peripheral neuropathy

Pyrazinamide - can cause hyperuricaemia - can result in gout. hepatitis

Ethambutol - optic neuritis. can cause colour blindness and reduce visual acuity

RIP - associated with hepatotoxicity

Question 28

What other management considerations are there for TB treatment?

Answer 28

1. ensure patients likely to have low concordance are observed taking medication
2. notify PHE
3. Test contacts for TB
4. test for other infectious conditions (HIV/Hep B,C)
5. patients with active TB need to be isolated until they are established on tx (2 weeks)