Clinicopathological differences between acute and chronic eosinophilic pneumonia

OBJECTIVE: Considerable confusion exists regarding the proper classification of idiopathic eosinophilic pneumonia (IEP). Furthermore, there are no reports describing the clinicopathological differences between the various forms of eosinophilic pneumonias. METHODOLOGY: The histological findings in acute eosinophilic pneumonia (AEP) and chronic eosinophilic pneumonia (CEP) were examined and the clinical and radiological features were contrasted with them. RESULTS: Radiologically, ground glass opacity and interlobular septal thickening were characteristic of the AEP cases, while air space consolidation was seen in all CEP cases. Histologically, interstitial oedema and fibrin deposition were prominent in the AEP cases. Type II cells were detached from the alveolar walls, although 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. CONCLUSIONS: An essential histological difference between AEP and CEP is the severity of basal lamina damage and the amount of subsequent intraluminal fibrosis. In AEP particularly, these findings explain the radiographical findings, as well as the rapid and complete improvement noted in such cases.