Extrinsic allergic alveolitis

Question 1

EAA- define

Answer 1

Extrinsic allergic alveolitis (EAA, also known as hypersensitivity pneumonitis) is a condition caused by hypersensitivity induced lung damage due to a variety of inhaled organic particles.

It is thought to be largely caused by:

• immune-complex mediated tissue damage (type III hypersensitivity)
• although delayed hypersensitivity (type IV) is also thought to play a role in EAA, especially in the chronic phase.

Question 2

causes

Answer 2

fungal spores/ avian proteins

eg

1. bird fanciers’ lung: avian proteins
2. farmers lung: spores of Saccharopolyspora rectivirgula (formerly Micropolyspora faeni)
3. malt workers’ lung: Aspergillus clavatus
4. mushroom workers’ lung: thermophilic actinomycetes*
5. bagassosis- sugar worker’s lung

Question 3

s/s

Answer 3

acute: occur 4-8 hrs after exposure,

• SOB,
• dry cough,
• fever, rigors, malaise
• crackles- no wheeze

chronic

• increasing dyspnoea
• wt loss
• T1 resp failure
• cor pulmonale

Question 4

ix

Answer 4

• blood tests to assess:
  
  • inflammatory markers
  • eosinophilia
  • specific precipitating antibodies
  • blood gas status
• chest radiography
  
  • no abnormality in the early disease
  • the lungs are small with some ground glass shadowing
  • with regular exposure to the allergen:
    
    • fluffy, nodular or streaky shadowing develops
    • the upper lobes are more commonly affected
    • these shadows represent areas of granuloma formation and fibrosis
    • in severe disease there may be areas of honeycomb lung
• lung function tests to assess:
  
  • the restrictive ventilatory defect
  • the decreased transfer factor during acute attacks
• allergen sensitivity tests
• tissue sampling:
  
  • bronchoalveolar lavage [high lymphocytes + mast cells]
  • biopsy

Question 5

mx

Answer 5

• Avoid exposure to the antigen responsible.
• Health and safety measures, for example improved methods of harvesting aimed at reducing the moisture content of hay.
• Oxygen in the acute case. Steroids have a role in severe cases, but steroid treatment is not an alternative to avoidance of exposure to the antigen.
• compensation may be payable