Hypersensitivity pneumonitis in adults

Hypersensitivity pneumonitis (also known as extrinsic allergic alveolitis) is a granulomatous condition associated with interstitial lung disease (ILD). Pathology is linked to repeated inhaled exposure to a sensitising antigen. Common forms of chronic hypersensitivity pneumonitis include bird fancier’s lung (exposure to proteins found in feathers or droppings) and hot tub lung (exposure to Mycobacterium avium complex).

A detailed history to identify potential exposures in both the work and home environment is recommended; measurement of specific circulating immunoglobulin G (IgG) antibodies may provide further information on the causative exposure. However, in approximately 40% of cases the causative exposure will not be identified.

The key to management is avoidance of the inciting environmental exposure because continued antigen exposure is associated with chronic disease and progression to ILD. Corticosteroids are recommended in acute, severe and progressive disease.