TB Flashcards
clinical features of pulmonary TB
- may be silent
- cough, sputum, weight loss, night sweats, haemoptysis, malaise
miliary TB
- occurs following haematogenous dissemination
- CXR; nodular opacities
- poor prognosis
primary TB
- First infection with MTb
- Macrophages phagocytose bacilli, it survives inside the macrophage and proliferates creating localised infection
- Most people at this stage are asymptomatic
- There is a delayed hypersensitivity reaction (about 3 weeks in) to bacilli proliferating inside macrophages, resulting in tissue necrosis and formation of a granuloma
- Granulomatous lesions consist of a central area of necrotic material (caseation – cheese like necrosis), surrounded by granulomatous inflammatory response. They exhibit fibrosis
- Caseated areas heal and many become calcified, some of these calcified nodules contain bacteria where the bacilli can lie dormant for many years
where does primary infection also spread to
nearby hilar lymph nodes
what is the primary TB lesions termed
Ghon focus
- small calcified nodule in the mid zone of the lung
2y TB
- majority of cases
- immune system contains infection
- associated with immunosuppression etc
what lesion is associated with 2y TB
Assmann focus
- Apical lesion that begins as a small caseating granuloma
- Similar histopathology to Ghon focus
diagnosis of latent TB
mantoux test
why may mantoux be false negative
patient has had BCG vaccination
PCR
allows identification of rifampicin and multi drug resistance
what is IGRA positive in
current, latent and previous untreated TB
IGRA
Quantification of how much gamma interferon is released from circulatory T cells in response to specific stimulus e.g. MTB
which type of hypersensitivity reaction is it
IV
CXR
may be normal bilateral hilar enlargement consolidation, cavitation, fibrosis and calcification
histology hallmark
caseating granuloma
