What the allergist should know about hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) appears to be an underdiagnosed condition. It may masquerade as recurrent pneumonia, idiopathic pulmonary fibrosis, Haman-Rich disease, or interstitial pneumonitis. The nature of the disease depends on the immunologic reactivity of the host and the intensity and chronicity of exposure. Causative agents include thermophilic organisms, mold, animals, and chemicals. Typical symptoms of cough, shortness of breath, chills, and fever typically begin four to six hours after exposure with a remittance on avoidance. Chest x-ray demonstrates interstitial pneumonitis, and pulmonary function testing shows a restrictive component. A precipitating IgG antibody is the immunologic hallmark. The immunopathogenesis appears to represent a combination of type III and IV immune responses. Identifying the offending antigen is vital so that appropriate environmental precautions can be carried out.