Tuberculosis

Question 1

What % of the world’s population is infected with TB?

Answer 1

33%

Question 2

Which mycobacterial species cause TB?

Answer 2

1. Mycobacterium tuberculosis
2. Mycobacterium bovis
3. Mycobacterium africanum
4. Mycobacterium microti

All are acid fast bacilli

Question 3

What is primary TB?

Answer 3

First infection with MTb

Once in the lung, alveolar macrophages ingest the bacteria and the bacteria proliferate within the macrophages

Inflammatory response occurs

Macrophages present the antigen to T-cells

Delayed hypersensitivity reaction occurs which leads to tissue necrosis and granuloma formation

Question 4

What is a Ghon focus?

Answer 4

The initial site of TB disease

Question 5

What term is used for a Ghon focus that also involves mediastinal LNs?

Answer 5

Ghon complex

Question 6

What term is used if a Ghon complex is calcified?

Answer 6

Ranke complex

Question 7

What % of patients develop active TB following contact with infection?

Answer 7

5%, increasing to 10% within the first year

Question 8

What is latent TB?

Answer 8

In most people who are infected by mycobacterium spp. the immune system contains the infection and the patient develops cell mediated immunity to the bacteria

= latent TB

Question 9

What is reactivation TB?

Answer 9

The majority of cases of TB are due to reactivation of a latent infection

Question 10

How many sputum samples are required to diagnose TB?

Answer 10

3

Question 11

Patient has TB, what does the chest x-ray show?

Answer 11

Consolidation ± cavitation

Pleural effusion

Widening of medisatinum due to lymphadenopathy

Question 12

Discuss LN TB

Answer 12

Other than the lungs, LNs are the most common site for TB infection

Most commonly extrathoracic LNs are infected as opposed to intrathoracic or mediastinal LNs

Usually presents as a firm non-tender enlargement of a cervical or supraclavicular LN

On CT the central area can appear necrotic

Question 13

What is miliary TB?

Answer 13

Miliary TB is TB that has spread throughout the body via the blood

This involves the CNS in 20% of cases

Chest x-ray shows multiple nodules which look like millet seeds (hence miliary)

Question 14

Which stain is most widely used to identify TB?

Answer 14

Auramine-rhodamine - more sensitive than Ziehl Neelsen

Question 15

Discuss TB treatment

Answer 15

If patient has fully sensitive TB - 6 months of treatment required (unless TB of the CNS in which case its 12mo)

Rifampicin, isoniazid, pyrazinamide, ethambutol

Question 16

Unwanted effects of rifampicin

Answer 16

Induces liver enzymes which may be transiently elevated in the serum of many patients

Stop the drug if serum bilirubin becomes elevated or if transferases are 3x elevated

Rifampicin can turn body secretions pink

Oral contraceptive will not be effective

Question 17

Unwanted effects of isoniazid

Answer 17

Very few unwanted effects with this drug

May cause neuropathy due to B6 deficiency but this is rare - common to give pyridoxine to counteract the neuropathy

Can cause hepatitis in <1% but this can be fatal if the drug isn’t stopped

Question 18

Unwanted effects of pyrazinamide

Answer 18

Hepatic toxicity (rare)

Reduces renal excretion of urate so may cause hyperuricaemic gout

Question 19

Unwanted effects of ethambutol

Answer 19

Dose related optic retrobulbar neuritis (inflammation of optic nerve) - presents as green colour blindness and reduced visual acuity as well as central scotoma (depressed vision in the centre/ area of focus)

Question 20

What is mutli-drug resistance in TB?

Answer 20

Resistance to rifampicin and isoniazid

Question 21

What is extensively drug resistant TB?

Answer 21

Resistance to rifampicin, isoniazid, fluroquinolones and at least one injectable agent e.g. amikacin, capreomycin or kanamycin

Question 22

How is latent TB diagnosed?

Answer 22

a) Tuberculin skin test - positive result is indicated by a delayed hypersensitivity after 48-72hrs following injection of purified protein derivative. If reaction is very strong, chest x-ray is done to check for active disease **MANTOUX test - may show wheal if patient has had BCG vaccine**
b) Interferon gamma release assays - relies on the fact that T-lymphocytes will release IFN-γ when exposed to specific antigens. Doesn’t distinguish between latent and acitve TB