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)
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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)
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3
Q

Pattern of disease in TB

A
  1. Primary TB - no previous exposure or poor immune system
  2. Secondary TB - previous exposure, sensitised
  3. Miliary TB
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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)
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5
Q

Outcomes of primary TB (3)

A
  1. Complete resolution (95%), only residual evidence of infection remaines
  2. Latent TB - viable organisms lie dormant in foci, infected but inactive - cannot transmit
  3. 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
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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
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7
Q

Outcomes of secondary TB (2)

A
  1. Healing - leaves central area of caseous necrotic material surrounded by a thick dense collagenous wall - calcifies - fibrocaseous TB (can reactivate)
  2. Progression - enlargement of apical lesion, continued tissue destruction, risk of erosion into vessels/airways - spread
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