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 lung – thermophilic 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
Investigations
- 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
Management
- Avoidance of allergen
- ?steroids
References
