Interstitial lung diseases in dogs and cats part II: Known cause and other discrete forms.

In addition to idiopathic interstitial pneumonias, interstitial lung diseases (ILDs) can occur secondary to known causes or be classified as discrete syndromes. Also known as diffuse parenchymal lung diseases, the ILDs represent a heterogenous group of non-infectious, non-neoplastic disorders characterized by varied patterns of inflammation and fibrosis. Characteristically associated with the true interstitium (i.e. the anatomic space lined by alveolar epithelial cells and capillary endothelial cells and the loose-binding connective tissue), it is important to understand ILDs are associated with pathology of the distal lung parenchyma and thus lesions can be bronchiolocentric or resemble alveolar filling disorders. Injury to the distal lung can occur via inhalation or hematogenous routes. This review will build on a proposed classification scheme adapted from human medicine to describe known cause and discrete forms of ILDs in dogs and cats.