Extrinsic allergic alveolitis

Question 1

Define extrinsic allergic alveolitis

Answer 1

Interstitial inflammatory disease of the distal gas-exchanging parts of the lung casued by inhalation of organic dusts. Also known as hypersensitivity pneumonitis. Abnormal healing response to injury leads to thickening and scarring of the lungs and might result in fibrosis

Question 2

Explain the aetiology/ risk factors for extrinsic allergic alveolitis

Answer 2

Inhalation of antigenic dusts induce a hypersensitivity response in susceptible px. These dusts include microbial and animal proteins, agricultural dust, and moulds. HP can also be caused by drugs such as methotrexate, nitrofurantoin, paint and metals.

Farmer’s Lung = mould hay containing thermophilic actinomycetes - Pseudomonas, Acinteobacter, Klebsiella

Pigeon Fancier’s Lung = caused by blood on bird feathers and feces

Maltworker’s Lung = barley or maltings containing Aspergillus clavatus

Risk factors:

• smoking
• viral infection
• exposure to dusts

Question 3

Summarise the epidemiology of extrinsic allergic alveolitis

Answer 3

UNCOMMON

2% of occupational lung disease

50% or reported cases affect farm workers

Geographical variation

Question 4

Recognise the symptoms of extrinsic allergic alveolitis

Answer 4

ACUTE:

• present 4012 hours after exposure
• reversible episodes of
  
  • cough
  • SOB
  • malaise, fever, myalgia
  • wheeze/productive cough if repeated high-level exp

CHRONIC:

• slowly increasing SOB
• decrease in exercise tolerance
• WT
• T1RF
• Cor pulmonale

Question 5

Recognise the presenting signs of extrinsic allergic alveolitis

Answer 5

ACUTE:

• Rapid shallow breathing
• pyrexia
• inspiratory crepitations

CHRONIC:

• Fine inspiratory crepitations
• Bibasilar rales
• Clubbing 50%

Question 6

Identify the appropriate investigations for extrinsic allergic alveolitis

Answer 6

Bloods:

• FBC - neutrophilia, lymphopenia
• ABG - reduced O2 + CO2
• ESR elevated
• Albumin decreased in chronic

CXR:

• normal in acute
• fibrosis in chronic
• infiltrates nodular or patchy

HRCT:

• ground glass shadowing and centrilobular nodules
• basal sparing

Pulmonary fx tests: restrictive (low FVC and low FEV1, preserved or increased ratio) or obstructive/restrictive, reduced total lung capacity

Bronchoalveolar lavage: increased cellularity and antibodies ± biopsy for infiltrates