examples of hypersensitivity pneumonitis (extrinsic allergic alveolitis).
Farmer’s lung is the prototypic example of a hypersensitivity pneumonitis. There are a wide variety of other hypersensitivity pneumonitides; some of the many other causes are listed in the belwo table.
These disorders represent an allergic lung reaction to various organic dusts that can initially manifest as capillary leak pulmonary edema, but chronically result in granulomatous interstitial fibrosis. In most cases, the offending antigens are microorganisms that grow within decaying vegetable matter.
Antigens from these organisms are delivered to the lung via inhalation of dust or aerosolized contaminated water.
Notable exceptions to this general concept are bird-related hypersensitivity pneumonitides. In bird fancier’s lung, hypersensitivity occurs against bird-related antigens, such as those found in bird feathers.
Causes of Hypersensitivity Pneumonitis
| EXPOSURES | CAUSES |
|---|---|
| Occupational | Organic dust |
| Farmer’s lung | Hay |
| Baker’s lung | Flour |
| Sugar cane worker’s lung | Sugar cane dust |
| Cotton worker’s lung | Cotton dust |
| Mushroom worker’s lung | Mushrooms |
| Hobbies | |
| Bird fancier’s lung | Bird feathers |
| Other exposures | |
| Down pillows and comforters | Bird feathers |
| Hot tubs | Aerosolized water |
| Humidifiers | Aerosolized water |
