Acute respiratory distress syndrome is a severe disease, the treatment and pathophysiology of which are not completely established. The pathology of
acute respiratory distress syndrome involves diffuse alveolar damage, which comprises severe alveolar epithelial cell damage, hyaline membrane formation, and festinate myofibroblast proliferation and
fibrosis in the intra-alveolar spaces. We performed a clinicopathologic investigation of 26 autopsy cases of diffuse alveolar damage. Three cases of them were diagnosed as
acute interstitial pneumonia that is idiopathic illness and resembles pathologically organizing diffuse alveolar damage. Immunohistochemical staining for types I and IV
collagen, alpha-smooth muscle actin, and Ki-67 was carried out, and the sites of myofibroblast proliferation and
type I collagen production were examined. All diffuse alveolar damage cases in the proliferative phase showed intra-alveolar myofibroblast proliferation. When diffuse alveolar damage was diagnosed pathologically as being due to severe
infection, all 7 patients showed
multiple organ dysfunction syndrome, whereas only 2 of 7 patients showed interstitial myofibroblast proliferation. When diffuse alveolar damage was attributed to
tumor treatment with
chemotherapy or to
drug toxicity, 3 of 16 patients showed
multiple organ dysfunction syndrome; 15 of 16 showed interstitial myofibroblast proliferation, 3 of 3
acute interstitial pneumonia patients did not show
multiple organ dysfunction syndrome; and 3 of 3
acute interstitial pneumonia showed marked interstitial myofibroblast proliferation. These results suggest that the pathophysiologic mechanism of diffuse alveolar damage caused by severe
infection is one of systemic circulation disturbance, although the mechanism underlying diffuse alveolar damage due to
tumor with
chemotherapy or
drug toxicity appears to involve
interstitial pneumonia-like lesions that are similar to
acute interstitial pneumonia.