Late-breaking abstract: Pathological analysis of acute exacerbation of idiopathic pulmonary fibrosis (IPF)

The patients with IPF show occasionally acute exacerbation in their clinical courses. However the details of pathology of acute exacerbation of IPF are not well investigated. Patients and methods: We studied clinico-pathologically 15 autopsy cases of acute exacerbation of IPF. The clinical symptoms of acute exacerbation were acute respiratory distress syndrome, but multiple organ failure (MOF) was not associated. The intervals of acute exacerbation and death were 3 days to 6 months. The triggers of acute exacerbation were the infection in 3 patients, myocardial infarction in 3 patients, surgical operation in 4 patients, chemotherapy for cancer in 1 patient and unknown in 7 patients. All patients were treated with steroid. Autopsied lung tissues were observed with light microscopy and immunohistochemistry. Results: The lungs of all cases showed pathologically some stage of diffuse alveolar damage (DAD) coincident with the period after acute exacerbation. In 11 cases, several stages of DAD were recognized in the lungs of same patient. DAD is found exclusively in the area without honeycombing. Though 5 cases showed also bud-type intra-alveolar fibrosis, which composed of accumulated myofibroblasts with few vessels and occasionally connected with ring-like DAD fibrosis. We do not interpret these findings as OP, but DAD. In addition to DAD, fibroblastic foci were frequently observed in 9 cases including the walls of honeycombing. The activity of IPF itself was estimated to be high in these patients. Conclusion: The pathological findings of acute exacerbation are DAD, and the several stages of DAD are characteristically observed in the same patient, which are similar to DAD caused by drug injury.