Lung Infections - Tuberculosis Flashcards
1
Q
Features of TB
A
- chronic pneumonia
- communicable, granulomatous
- caused by Mycobacterium tuberculosis
- initial infection usually inhaled, but does not only affect lungs
- within the lung, spread via bronchi, lymphatic, into pleura, blood (miliary)
2
Q
Features of Mycobacteria
A
- slender rod-shaped, waxy cell wall
- resistant to destruction by neutrophils
- only macrophages can phagocytose & contain mycobacteria, but it can still proliferate
- own cells killed while killing mycobacteria - cavities
- bind Ziehl-Neelsen stain, resist discolouration (AFB)
3
Q
Pattern of disease in TB
A
- Primary TB - no previous exposure or poor immune system
- Secondary TB - previous exposure, sensitised
- Miliary TB
4
Q
Pathogenesis in primary TB
A
- inhalation - infection & necrosis at lung periphery, just beneath the pleura (Ghon focus)
- heal or spread to involved local lymph nodes at hilum (Ghon focus + affected lymph nodes = Ghon complex)
- enlarge through granulomatous inflammation & caseation (necrosis)
5
Q
Outcomes of primary TB (3)
A
- Complete resolution (95%), only residual evidence of infection remaines
- Latent TB - viable organisms lie dormant in foci, infected but inactive - cannot transmit
- Progressive primary TB - severe pneumonia & dissemination, continuining enlargement of caseating granulomas in lymph nodes, spread by enlarging nodes eroding through pleura, wall of bronchus/vessel
6
Q
Pathogenesis of secondary TB
A
- exogenous infection (acq new organisms) or reactivation of primary complex
- usually in the apex of the lung - Assmann focus - central area of caseous necrosis surrounded by granulomas
- immune system recognises infection, rapid mobilisation of defence reaction - tries to contain it, less lymph node involvement
- destruction of lung tissue + granulomatous inflammation - cavitation
7
Q
Outcomes of secondary TB (2)
A
- Healing - leaves central area of caseous necrotic material surrounded by a thick dense collagenous wall - calcifies - fibrocaseous TB (can reactivate)
- Progression - enlargement of apical lesion, continued tissue destruction, risk of erosion into vessels/airways - spread