Hypersensitivity Pneumonitis

Excerpt

Hypersensitivity pneumonitis (HP) classified as an interstitial lung disease is characterized by a complex immunological reaction of the lung parenchyma in response to repetitive inhalation of a sensitized allergen. The name HP defines the disease more appropriately than the previous term extrinsic allergic alveolitis, as the inflammation involves not only the alveoli but the bronchioles as well. The severity of the disease and clinical presentation varies depending on the inhaled antigen and quantity. The first detailed clinical descriptions of the disease came out in 1932 describing symptoms in workers exposed to a fungus on Maple bark at a Michigan company and agricultural workers exposed to moldy hay in England. Since these initial observations, numerous exposures have been described from all over the world that causes HP.

Traditionally it has been classified into acute, sub-acute and chronic forms based on the time course and the presentation. But more recently classifying it to Acute or Inflammatory HP (symptoms less than six months) and Chronic or fibrotic HP has been proposed based on clinical, radiologic and pathologic characteristics.