Extrinsic Allergic Alveolitis

Question 1

def

Answer 1

interstitial inflammatory disease of the distal gas-exchanging parts of the lung caused by inhalation of organic dusts
also know as hypersensitvity pneumonitis

Question 2

aetiology

Answer 2

inhalation of antigenic organic dusts which induces a hypersensitivity response (combination of TIII antigen-antibody complex hypersensitivity reaction & TIV granulomatous lymphocytic inflammation)

Question 3

examples of extrinsic allergic alveolitis

Answer 3

1 farmers lung - mouldy hay containing thermophilic actinomycetes
2 pigeon fanciers lung - bloom on bird feathers & excreta
3 mushroom worker’s lung - compost containing thermophilic actinomycetes

Question 4

epi

Answer 4

uncommon
2% of occupational lung diseases
50% of reported cases affect farm workers (4-10 per 100,000PA

Question 5

history

Answer 5

ACUTE
-presents 4-12h post-exposure
-reversible episodes of dry cough, dyspnoea, malaise
-wheeze & productive cough may develop on repeat exposure
CHRONIC
-poorly reversible manifestation in some
-slowly increasing breathlessness & decreasing exercise tolerance
-exposure is usually chronic, low level

full occupational history, enquiry into hobbies, pets

Question 6

examination

Answer 6

ACUTE
-rapid shallow breathing
-pyrexia
-inspiratory crepitations
CHRONIC
-fine inspiratory crepitations

Question 7

investigations

Answer 7

1 bloods
-FBC (neutrophilia, lymphopenia)
-ABG (low PO2, low PCO2)
2 serology
-precipating IgG to fungal/avian antigens - however not diagnostic
3 CXR
-often normal in acute episodes, however may show 'ground glass' appearance with alveolar shadowing or nodular opacities in middle/lower zones
-in chronic cases, prominent fibrosis in upper zones
4 high resolution CT thorax
-detects changes before CXR
-patchy 'ground glass' shadowin & nodules
5 pulmonary function tests
-restrictive ventilatory defect
-decreased FEV1
-decreased FVC1
-normal/increased ratio