Hypersensitivity pneumonitis in children.

Hypersensitivity pneumonitis in children is an underrecognized form of immune-mediated interstitial lung disease that results from repeated exposure to the inhalation of organic antigens. Because overt disease develops in only a small percentage of exposed individuals, complex interactions between the nature of the antigen, the intensity and duration of the exposure, and the host response in susceptible individuals are most likely involved. In most reported pediatric cases, hypersensitivity pneumonitis results from exposure to avian antigens, but it has also been seen with exposure to molds and methotrexate. The diagnosis is established by documented exposure, compatible clinical presentation, and consistent radiologic features; it is supported by positive precipitating antibodies, lymphocytosis in bronchoalveolar lavage fluid, and characteristic histologic changes on lung biopsy. Treatment consists of antigen avoidance in all cases, and corticosteroids in severe cases. The prognosis is excellent when prompt recognition and treatment are initiated.