Extrinsic allergic alveolitis

Question 1

Define extrinsic allergic alveolitis

Answer 1

Hypersensitivity pneumonitis = interstitial inflammatory disease of the distal gas-exchanging parts of the lung caused by inhalation of organic dusts

Question 2

Explain the aetiology / risk factors of extrinsic allergic alveolitis

Answer 2

Inhalation of antigenic organic dusts containing microbes or animal proteins induce a hypersensitivity response

Combination of type 3 (antigen-antibody complex hypersensitivity reaction) and type 4 (granulomatous lymphocytic inflammation)

Examples:
Farmer’s lung - Mouldy hay (containing thermophilic actinomycetes)

Pigeon fancier’s lung - Bloom on bird feathers and excreta

Mushroom worker’s lung - Compost (containing thermophilic actinomycetes)

Humidifier lung - Water-containing bacteria

Maltworker’s lung - Barley or maltings

Exposure to metal working fluid

SMOKING INCREASES RISK

Question 3

Summarise the epidemiology of extrinsic allergic alveolitis

Answer 3

Uncommon
High correlation with occupation
o	2% of occupational lung diseases
o	50% affect farm workers – incidence of up to 10 in 100,000/year
o	Marked geographical variation

Question 4

Recognise the presenting symptoms of extrinsic allergic alveolitis

Answer 4

Acute – 4-12hrs post exposure
o	SOB
o	Cough – almost always non-productive
May become productive with repeat high-level exposures
o	Malaise
o	Fever/chills

Chronic – chronic, low level exposure
o	Slowly progressive SOBOE
o	Decreased exercise tolerance
o	Dry cough 
o	Weight loss

Question 5

Recognise the signs of extrinsic allergic alveolitis on physical examination

Answer 5

Acute (4-6 hours after exposure)
o	Bibasilar/diffuse rales
o	SOB - rapid shallow breathing
o	Pyrexia
o	Rigors

Chronic
o Fine inspiratory crepitations
o Clubbing

Question 6

Identify appropriate investigations for extrinsic allergic alveolitis

Answer 6

FBC: leucocytosis, neutrophilia
ESR: elevated
Albumin: low

Serology - Precipitating IgG to antigen present

CXR – 1st line
Acute - Often normal, Ground glass appearance with alveolar shadowing in middle/lower zones, Reticulonodular shadowing, Honeycomb appearance, Cor pulmonale

Chronic
Prominent fibrosis in upper zones

High resolution CT thorax - GS (Detects early changes before CXR), Patchy ground glass shadowing and nodules

Spirometry
Restrictive ventilatory defect: low FEV1, (more) low FVC

Bronchoalveolar lavage
Increased cellularity with raised CD8+ suppressor T cells