Tuberculosis Flashcards
What is a GHON FOCUS?
Lesion: granuloma formation
Initial infection with Mycobacterium tuberculosis in an immunocompetent individual usually occurs in an upper region of lower lobe of the lung
What is GHON COMPLEX?
= early Ghon focus + lymph node lesion
What happens to a Ghon complex over time?
These lesions undergo healing and over time usually evolve to fibro-calcific nodules.
Where does a Ghon focus usually reside?
= initial site of infection
usually in peripheral mid zone
What is caseous necrosis?
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)
How may post-caveating granuloma turned cavity be seen clinically?
on a CXR
usually in the apex region of the lung
seen as dark holes with a distinct rim (border of granuloma)
What is Miliary TB?
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
What is intestinal TB?
can occur as SECONDARY to pulmonary TB from swallowing infected sputum
PRIMARY intestinal TB occurs after injecting M.bovis infected milk
What are the features of TB in brain/meninges?
- 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
What are associated complications of miliary TB?
- Potts disease
- Scrofula (TB in LNs)
What do Koch’s postulates define?
criteria designed to establish a casual relationship between microbe and disease (= germ theory)
What are the criteria detailed in ‘Koch’s postulates’?
- 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
What are the exceptions to’ Koch’s postulates’?
- 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)
Which staining methods can be used to identify AAFB in sputum samples?
- Ziehl-Neelsen stain
microscopy + acid fast - auramine stain
fluorescence microscopy
What is the purpose of using GeneXpert for TB Ix?
will detect TB DNA in sputum samples
quick
can also perform sequencing to identify drug sensitivity profiles
