Pulmonary histopathology in dalmatians with familial acute respiratory distress syndrome (ARDS).

The histopathological changes in the lungs of 12 related Dalmatians with idiopathic acute respiratory distress syndrome (ARDS) are described. Affected dogs had multiple foci of marked atypical hyperplasia and squamous metaplasia of the bronchiolar epithelium, patchy ongoing fibrosis with myofibroblastic metaplasia, smooth muscle hyperplasia and occasional honeycombing of alveolar walls, and hyperplasia of atypical type II pneumocytes. There was an abrupt transition between these proliferative lesions and areas of acute alveolar oedema with hyaline membranes in partially normal lung. Diseased areas were associated with moderate lymphohistiocytic interstitial inflammation. Immunohistochemical labelling for cytokeratin expression indicated that the metaplastic epithelium was of bronchiolar origin and that it extended into peribronchiolar alveolar spaces. Some of the bronchiolar lesions were pre-neoplastic and one adult dog suffered from bronchoalveolar carcinoma. These lesions are compared with the two forms of idiopathic interstitial pneumonia reported as causes of ARDS in man: acute interstitial pneumonia (AIP) and acute exacerbation of idiopathic pulmonary fibrosis (IPF). The observed lesions in the Dalmatians are distinct from the diffuse alveolar damage that characterizes AIP, but show some histological similarities to the usual interstitial pneumonia (UIP) that occurs in IPF with acute exacerbation in man. UIP has not previously been described in the dog.