TB

Question 0

Describe the pathology of TB infections

Answer 0

1. Droplets containing tubercle bacilli are inhaled, enter the lung and travel to alveoli
2. Tubercle bacilli multiply in alveoli –> infection
3. A few tubercle bacilli enter bloodstream and spread throughout body
4. Within 2-8wks, activated macrophages surround the tubercle bacilli, forming a barrier shell that keeps the bacilli contained and under control (LTBI)
5. If the immune system can’t control the tubercle bacilli –> multiply rapidly and cause TB disease

Question 1

Describe the microbiology of mycobacterium tuberculosis

Answer 1

Gram resistant, acid fast rods

Question 2

Describe the primary and post-primary changes in TB

Answer 2

Primary - Ghon’s focus, very soon after infection

Post-primary - many years after infection

Question 3

Explain the terms ‘Ghon’s focus’ and ‘Ghon’s complex’

Answer 3

Ghon’s focus - primary lesion that develops in non immune host, granulomatous inflammation only detectable by CXR if it calcifies or grows
Ghon’s complex - calcified focus of infection and an associated lymph node

Question 4

Define the typical clinical presentation and radiographic changes in non-respiratory TB (including lymph node TB, orthopaedic TB, TB meningitis, other sites)

Answer 4

Symptoms - fever, night sweats, cough, haemoptysis

Signs - non-specific, no chest signs, CXR abnormal, crackles, cavitation

Question 5

Describe the investigations when a patient has suspected TB

Answer 5

CXR
Sputum (x3)
Bronchoscopy
Biopsy

Question 6

Describe some of the signs that may be present on a patient with TB

Answer 6

Apex often involved
Ill defined patchy consolidation
Cavitation within consolidation
Healing –> fibrosis

Question 7

Describe the principles of management of TB (including drugs, toxicity, schedules and problems with compliance)

Answer 7

Combination of 4 drugs (Rifampicin, isoniazid, pyrazinamide, ethambutol)
Toxic to hepatocytes
6 months or more
Compliance necessary to prevent resistant strains developing

Question 8

Describe the role of BCG vaccination

Answer 8

Intradermal injection of live, attenuated TB
Leaves scar
Causes skin lesion
Provides immunity, hypersensitivity
Immunity lasts 10-15 years

Question 9

List come of the causes for LTBI –> TB

Answer 9

Infection with HIV
Substance abuse
Organ transplant 
Diabetes mellitus
Low body weight

Question 10

List common sites for TB spread

Answer 10

Brain
Lung
Larynx
Lymph nodes
Pleura
Bone
Spine
Kidney

Question 11

Describe the condition of Miliary TB

Answer 11

Bacilli spreads through bloodstream
During primary/reactivation
Lungs involved (few respiratory symptoms)
Multiple organs involved