[Clinicopathological differences between acute and chronic eosinophilic pneumonia].

Considerable confusion exists regarding the proper classification of idiopathic eosinophilic pneumonia (IEP). In addition, there are no reports that reveal clinicopathological differences between the various eosinophilic pneumonias. A problem persists in describing what the essential histological differences are between the different types of IEP. In this context, we examined the histological findings of acute eosinophilic pneumonia (AEP) and chronic eosinophilic pneumonia (CEP) and contrasted them with the clinical features and radiological findings. Radiologically, ground glass opacity and interlobular septal thickening were characteristic of the AEP cases studied, while air space consolidation was seen in all CEP cases. Histologically, interstitial edema and fibrin deposition were prominent in the AEP cases. Type II cells were detached from the alveolar walls, though the basal lamina was predominantly intact. In CEP, in addition to cellular infiltration, there was prominent intraluminal fibrosis. Disruption of the basal lamina was observed and nests of intraluminal fibrosis were directly adjacent and connected to the alveolar walls. From these findings, we conclude that the histological differences between AEP and CEP are the severity of basal lamina damage, the amount of subsequent intraluminal fibrosis, and the severity of interstitial edema. Especially in AEP, interstitial edema is an essential histological finding and this finding explains the acute onset, and the radiographic findings, as well as the rapid and complete improvement noted in such cases.