Acute interstitial pulmonary fibrosis. Comparative light and electron microscopic study of 19 cases. Pathogenic and therapeutic implications.

Comparative light and electron microscopic studies of the lung were performed in 19 cases of diffuse acute interstitial fibrosis with various etiologies. Our observations emphasize the relation between hyaline membranes (HM) and the evolution of fibrosis. HM formation is due to fibrinous exudates and epithelial necrosis. This phenomenon recurs during the evolution of the disease and appears to be responsible for new waves of fibrosis. Its pathogenesis (humoral or neurovascular ...) remains hypothetical. Modifications of the alveolar epithelium consecutive to septal fibrosis can be clearly distinguished from "fibrinoid necrosis" -type lesions, which results in HM. The formation of HM is accompanied by fibroblastic stimulation which proceeds in spite of epithelial regeneration. The exact stimulus for the proliferation and collagen hypersecretion of fibroblasts remains to be determined. The use, in association with corticosteroid treatment, of a structural analogue of L lysine, acexamic acid, to impede collagenesis reveals encouraging perspectives for improved therapy.