Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a syndrome caused by an exaggerated immune response to the inhalation and subsequent sensitization to a variety of environmental antigenic particles. The pathogenesis remains unclear; however, a “two-hit hypothesis” implicating a pathologic interaction between an environmental antigen and the immune system of a susceptible host seems likely as only a minority of the exposed individuals develop HP. The presentation may be acute, as in bird fancier’s lung, the classical form of HP, or more insidiously as the subacute form of chronic HP caused by repeated low-level antigenic exposure. Despite these categorizations, there is frequently an overlap between the clinical entities and no guaranteed linear progression through the different pathologic stages. Prompt diagnosis is crucial, and is based on an exposure history, precipitating antibodies to the offending antigen, and a combination of clinical, radiologic, and physiological findings. The mainstay of treatment is allergen avoidance, but systemic steroids are of value for both the subacute and the chronic forms, although they do not alter the long-term outcome. This review summarizes the current knowledge of the pathophysiology of HP and the main entities in the differential diagnosis.
Source: Clinical Pulmonary Medicine - Category: Respiratory Medicine Tags: Topics in Pulmonary Medicine Source Type: research