MI: Mycobacterial Diseases Pt.2

Question 1

What is the issue with culturing TB?

Answer 1

It takes up to 6 weeks

Question 2

What is the histological hallmark of TB?

Answer 2

Caseating granulomas

Question 3

What is NAAT and why is it useful?

Answer 3

• Nucleic acid amplification test
• Allows speciation and the detection of drug resistance mutations
• Rapid

Question 4

What are the screening tests for latent TB

Answer 4

Tuberculin skin test

Interferon gamma release assay

Question 5

What is the tuberculin skin test (Mantoux test) and how does it work?

Answer 5

A sample of tuberculin is injected intradermally and left for 48-72 hours to observe the response

Type IV hypersensitivity (T cell) response to antigen

Question 6

What are the disadvantages of the tuberculin skin test?

Answer 6

• Cross-reacts with BCG
• Cannot distinguish between active and latent TB
• False negative in immunosuppressed individuals

Question 7

What is an IGRA assay?

Answer 7

• Uses M. tuberculosis specific antigens to stimulate T cell IFN-gamma production which is then measured using ELISA

Question 8

What are the advantags and disadvantges of IGRA assay?

Answer 8

No cross reactivity with other strains

Does not distinguish between latent or active TB

Question 9

What do you do if screening tests are positive?

Answer 9

CXR (looks for active TB)

if CXR normal - treat with latent TB protocol

Question 10

What is the treatment of latent TB

Answer 10

• 3 months of isoniazid plus rifampicin
• Or 6 months of isoniazid

Question 11

What is the treatment of active TB

Answer 11

• Initiation phase: rifampicin, isoniazid, pyrazinamide, ethambutol for 2 months
• Continuation phase: rifampicin plus isoniazid for 4 months

Question 12

List some side-effects of:

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

Answer 12

1. Rifampicin
   
   • Raised transaminases
   • CYP450 induction
   • Orange secretions
2. Isoniazid
   
   • Peripheral neuropathy
   • Hepatotoxicity
3. Pyrazinamide
   
   • Hepatotoxicity
4. Ethambutol
   
   • Visual disturbance

Question 13

What drug is given to prevent peripheral neuropathy from isoniazid?

Answer 13

Pyridoxine

Question 14

What is DOT?

Answer 14

Direct observation therapy

Question 15

What is multi-drug resistant TB?

Answer 15

Resistant to rifampicin and isoniazid

Question 16

What is extremely drug resistant TB?

Answer 16

Resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable

Question 17

What are the diagnostic challenges of HIV and TB coinfection?

Answer 17

• Clinical presentation is less likely to be classical
• Symptoms may be absent if CD4+ count is low
• More likely to have extra-pulmonary manifestations
• Tuberculin skin test more likely to give false-negative
• Low sensitivity for IGRAs

Question 18

What are the treatment challenges of HIV and TB coinfection?

Answer 18

• Timing of treatment
• Drug interactions
• Overlapping toxicities
• Duration of treatment