Tuberculosis

Question 1

What is a GHON FOCUS?

Answer 1

Lesion: granuloma formation
Initial infection with Mycobacterium tuberculosis in an immunocompetent individual usually occurs in an upper region of lower lobe of the lung

Question 2

What is GHON COMPLEX?

Answer 2

= early Ghon focus + lymph node lesion

Question 3

What happens to a Ghon complex over time?

Answer 3

These lesions undergo healing and over time usually evolve to fibro-calcific nodules.

Question 4

Where does a Ghon focus usually reside?

Answer 4

= initial site of infection

usually in peripheral mid zone

Question 5

What is caseous necrosis?

Answer 5

usually found in the centre of the granuloma
death of contents
produces ‘caseous’ consistency
eventually this will be replaced by a cavity (where healthy tissue existed pre-infection)

Question 6

How may post-caveating granuloma turned cavity be seen clinically?

Answer 6

on a CXR
usually in the apex region of the lung
seen as dark holes with a distinct rim (border of granuloma)

Question 7

What is Miliary TB?

Answer 7

disseminated TB infection
Typically occurs when resistance to mycobacterial infection is poor

Often in children as consequence of primary disease.

The small millet seed sized granulomas in this lung are typical for miliary tuberculosis

Question 8

What is intestinal TB?

Answer 8

can occur as SECONDARY to pulmonary TB from swallowing infected sputum

PRIMARY intestinal TB occurs after injecting M.bovis infected milk

Question 9

What are the features of TB in brain/meninges?

Answer 9

• thickened and opaque meninges
• small tubercle present within brain
• may develop into meningitis

Common childhood complication of military TB, but rarely seen in those who’ve had BCG

Question 10

What are associated complications of miliary TB?

Answer 10

• Potts disease

- Scrofula (TB in LNs)

Question 11

What do Koch’s postulates define?

Answer 11

criteria designed to establish a casual relationship between microbe and disease (= germ theory)

Question 12

What are the criteria detailed in ‘Koch’s postulates’?

Answer 12

• demonstrate that organism is in all lesions in all cases
• isolate organism and cultivate in in pur culture ex vivo
• produce same disease if pure culture is injected into a naive individual
• recover microbe from nascently infected host

Question 13

What are the exceptions to’ Koch’s postulates’?

Answer 13

• not all organisms can be cultured ex vivo (M. leprae, syphillis, some viruses)
  [BUT can detect their genome by PCR]
• not applicable to all diseases
  (cancers associated with viruses, EBV, HepB)

Question 14

Which staining methods can be used to identify AAFB in sputum samples?

Answer 14

• Ziehl-Neelsen stain
  microscopy + acid fast
• auramine stain
  fluorescence microscopy

Question 15

What is the purpose of using GeneXpert for TB Ix?

Answer 15

will detect TB DNA in sputum samples
quick
can also perform sequencing to identify drug sensitivity profiles

Question 16

What is the treatment for TB?

Answer 16

2 for 4:

• rifampicin
• isoniazid

THEN

4 for 2:

• rifampicin
• isoniazid
• ethambutol
• pyrazinamide

Question 17

What are the adverse reactions of rifampicin?

Answer 17

• hepatitis
• rash
• GI upset
• intermittent Rx: flu like symptoms
• drug interactions
  (OCP/prednisolone)
• Orange pee and other fluids

Question 18

What are the adverse reactions of isoniazid?

Answer 18

• rash
• peripheral neuropathy (give vit B6 supplements)
• hepatitis

Question 19

What are the adverse reactions of ethambutol?

Answer 19

dose related neuropathy

Ishihara screening for colour blindness

Question 20

What are the adverse reactions of pyrazinamide?

Answer 20

• hepatitis
• facial flushing
• rash
• nausea & anorexia
• arthralgia
• high uric acid

Question 21

What are the main expected checkpoints following initiation of Rx?

Answer 21

2 wks: non-infectious, feeling better, no temperature
1 mnth: gaining weight and sputum smear negative
2 mnth: sputum culture negative

Question 22

What are the main reasons why a Mantoux test may be ‘false negative?’

Answer 22

• delayed response
• HIV
• protein malnutrition
• sarcoid
• intercurrent viral infections
• corticosteroids
• delayed result in indochinese

Question 23

How is sarcoidosis distinguished from TB?

Answer 23

in sarcoid:

• tuberculin test -ve
• granulomas seen on CXR and biopsy

Question 24

What are the advantages of the IGRAs?

Answer 24

• sensitive, capable of detecting single cell secreting IFNg
• more specific Ag (than PPD in Mantoux)

Question 25

What are the disadvantages of IGRAs?

Answer 25

- requires living cells - time consuming and aseptic cleanliness needed - "false positives" from other mycobacteria - detects exposure not active infection - false negatives, assay issues