Hypersensitivity Pneumonitis: A Fibrosing Alveolitis Produced by Inhalation of Diverse Antigens

Publication date: Available online 15 November 2018

Source: Journal of Allergy and Clinical Immunology

Author(s): Paul A. Greenberger

Abstract

Hypersensitivity pneumonitis (HP) is a T_H1 lymphocyte biased fibrosing alveolitis that is caused by antigens ranging from avian excreta, fungi, thermophilic bacteria, and protozoa to reactive chemicals found in the workplace. Mimicking a viral syndrome, acute exposures to inciting antigens cause abrupt onset of non-productive cough, dyspnea, chills, with arthralgias or malaise usually from 4-8 hours later so that the temporal relationship between antigen exposure and symptoms may be unsuspected. The histology of HP reveals prominent lymphocyte infiltrates that thicken the alveolar septa with poorly formed granulomas or giant cells. Broncholalveolar lavage demonstrates > 20% lymphocytes in nearly all patients. Abnormalities on high resolution computerized tomography examinations range from nodular, centrilobular opacities in acute/subacute disease to increased reticular markings and honeycombing fibrosis, which typically are predominant in the upper lobes, in advanced disease. Descriptors include "mosaic attenuation" and "ground-glass" opacities. Repeated episodes can result in nodular pulmonary infiltrates and suspected nonspecific interstitial pneumonia or idiopathic pulmonary fibrosis. Clinicians require a high level of suspicion to make an early diagnosis of HP before extensive pulmonary fibrosis or restrictive lung disease has occurred.

https://ift.tt/2K7QabX