Extrinsic allergic alveolitis

Extrinsic allergic alveolitis, AKA hypersensitivity pneumonitis, is a group of immune-mediated lung diseases in which repeated inhalation of allergens results in type III and type IV hypersensitivity reactions with granulomatous inflammation

Most cases take years of repeated exposure to the allergen before EAA develops; once it does, symptoms tend to occur 4 to 8 hours after inhalation of an allergen: 
  • Dyspnoea 
  • Unproductive cough 
  • Fever 
  • Myalgia

Chronically patients have permanent dyspnoea, emphysema, pulmonary fibrosis and weight loss, with the potential to progress to respiratory failure and cor pulmonale. 

Forms of extrinsic allergic alveolitis include: 
  • Farmer’s lungthermophilic actinomycetes, Saccharopolyspora rectivirgula (Micropolyspora faeni), and Aspergillus umbrosi 
  • Bird fancier lung 
  • Malt worker’s lung – aspergillus species
  • Hot tub lung - mycobacterium avium complex
  • Japanese summer disease – various fungi from moldy houses – t. cutaneum

  • CXR – pulmonary infiltrates; fibrosis upper lobes > lower lobes
  • HRCT ground glass shadowing, gas trapping
  • Lung function tests: 
    • Spirometry – restrictive pattern
    • Diffusing capacity for carbon monoxide – decreased 
  • Bronchial lavage – initially neutrophils then lymphocytes

  • Avoidance of allergen
  • ?steroids

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