Airflow obstruction and airway lesions in hypersensitivity pneumonitis

Peripheral airways of lung biopsies from patients with HP commonly show several morphologic changes, including inflammation, fibrosis, or both. In most cases, damage of the airways is parallel to damage of surrounding parenchyma and the functional result is lung restriction, perhaps with alterations in the so-called "small airway tests." Chronic cough and phlegm also are more common in subjects exposed to organic antigens. Overt airflow obstruction is present in a number of patients with HP, and they usually have other risk factors, such as asthma, cigarette smoking, or dust inhalation. There are limited studies of patients who have HP and CAO but not concomitant risk factors for CAO, making it difficult to reach any firm conclusion about their association. In most cases, the lesion that could explain severe airflow obstruction seems to be located in bronchioles but, based on several clinical reports, there is the possibility that HP occasionally ends in emphysema.