ABSTRACT
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is a complex syndrome caused by repeated inhalation of and sensitization to finely dispersed antigens. These antigens encompass a wide variety of organic particles including fungi, bacterial, protozoal, animal and insect proteins, and certain small molecular weight volatile and non-volatile chemical compounds. Pathologically the disease is characterized by a diffuse and predominantly mononuclear cell inflammation of the alveoli, terminal bronchioles and interstitium. However, in some instances, this granulomatous, lymphocytic infiltrate can lead to the development of pulmonary fibrosis.
