[Bronchial involvement in hypersensitivity pneumonitis]

International audience; Hypersensitivity pneumonitis is a respiratory disease resulting from the inhalation of antigens to which the exposed subject has been previously sensitized. Hypersensitivity pneumonitis is characterized by a diffuse and predominantly mononuclear cell inflammation of the alveolar regions that involves the small airways in most cases. It explains the presence of mosaic attenuation and expiratory air trapping at HRCT Scan. Chronic bronchitis, an obstructive defect at lung function tests and emphysema as long-term outcome are frequent consequences of this bronchial involvement.