Tuesday, 7 September 2010

MRCP revision battle 4.2: Extrinsic Allergic Alveolitis

This is inflammation of lung tissue due to hypersensitivity to an allergen.  To get more scientific, it is a Gell and Coombs type 3 reaction acutely and a type 4 reaction chronically.

Clinically, an acute reaction occurs 4-6 hours post exposure and manifests as fever, rigors, dry cough, dyspnoea and myalgia.  Auscultation of the lungs might reveal crackles but no wheeze.

Chronically EAA causes dyspnoea, weight loss and can eventually lead to type 1 respiratory failure and cor pulmonale.

There are several different 'flavours' of EAA, each precipitated by something different.  These include:
  • Farmers lung: micropolyspora faeni or thermoactinomyces vulgaris or Saccharopolyspora rectivirgula
  • malt workers lung: aspergillos clavatus
  • mushroom workers lung: thermophilic actinomycetes
or, more modernly:
  • hot tub lung: mycobacterium avium in poorly maintaned hottubs!

A CXR acutely might show mid-zone mottling; chronically upper zone fibrosis might be seen.  It can also be a cause of bilateral hilar lymphadenopathy (remember battle 3.1?)

Spirometry gives a restrictive picture and lavage will show lymphocytes.

Treatment is oxygen, possibly steroids.

Allons-y to battle 4.3!