TB & Mycobacteria

Question 1

How does TB typically present?

Bonus: Other ways it could present in immunosuppressed pts?

Answer 1

Fever, night sweats, weight loss
Cough + haemoptysis

In immunosuppression:
(Brain) Subacute meningitis
(Spine) Pott’s disease: Back pain, discitis, vertebral destruction

Question 2

What are classic histological lesions associated with TB?

Answer 2

CASEATING granulomas. The centre of the granulomas undergo necrosis due to hypoxia/free radicals. Under microscopy it looks white and complete loss of cellular architecture.

Non-caseating granulomas are seen in sarcoidosis, Crohn’s and leprosy.

Question 3

How do you screen for latent TB?

Answer 3

Mantoux test (Tuberculin skin test)

<6mm = Negative - unvaccinated should be given BCG

6-15mm = DON’T give BCG, could be due to previous BCG/infection

>15mm = Strongly +ve for TB infection

IGRA shows exposure (active/latent but NOT BCG).

Used when:

• Mantoux +ve OR
• Mantoux may be false negative
  
  • Miliary TB
  • Sarcoidosis
  • HIV
  • Lymphoma
  • <6 months

Question 4

Investigations for TB?

Answer 4

CXR: Upper lobe cavity, Bilateral hilar lymphadenopathy

*Miliary TB: disseminated spread on CXR

• *Sputum smear (3 samples needed)**:
  1. Acid-fast bacilli on Ziehl-Neelson stain
  2. Sensitivity 50-80% but REDUCED in HIV pts to 20-30%

Screening for latent TB = Mantoux test

<6mm = Negative - unvaccinated should be given BCG

6-15mm = DON’T give BCG, could be due to previous BCG/infection

>15mm = Strongly +ve for TB infection

IGRA shows exposure (active/latent but NOT BCG), used for

Question 5

Once infected, which patients with TB show symptoms?

Answer 5

Infection usually asymptomatic - becomes latent in Gohn focus or granuloma

Reactivates (e.g. when immunosuppressed) and becomes symptomatic

Primary TB infection = less common and IS symptomatic. Risk factor is immunosuppression.

Post-primary TB = symptomatic as well

Question 6

Risk factors for TB?

Answer 6

Travel to South Asia/Eastern europe
HIV
Homeless
IVDU
TB contact

Question 7

Treatment for TB?

Answer 7

• *RIPE**:
• *R**ifampicin
• *I**soniazid
• *P**yrazinamide
• *E**thambutol

Continue all 4 for 2 months
Then R + I (first 2) for another 4 months

Question 8

Side effects of TB medications?

Answer 8

SEs:
R - orange secretions
I - peripheral neuropathy
P - hepatotoxic
E - optic neuritis

Question 9

What is the vaccine for TB?

Answer 9

BCG vaccine

Attenuated strain of M.bovis given to high risk pts.

It is a LIVE VACCINE hence contraindicated in immunosuppressed

Question 10

Name 4 other mycobacterial diseases and their key features

Answer 10

Leprosy: M. Leprae - Nerve thickening, skin depigmentation, nodules, trophic ulcers. Lifelong illness.

Mycobacterium Avium-intracellulare complex: disseminated infection in immunocompromised. resembles TB if underlying lung disease

Mycobacterium Marinarum (Fish tank granuloma): aquarium owners

Mycobacterium ulcerans (Buruli ulcer): tropics/Australia, painless nodules progressing to ulcers