Histopathology of Eosinophilic Pneumonia

Although nonprominent, some eosinophilic microabscesses and a nonnecrotizing vasculitis are common in idiopathic chronic eosinophilic pneumonia (ICEP) and idiopathic acute eosinophilic pneumonia (lAEP). Parenchymal necrosis or interstitial fibrosis is seldom present, and most eosinophilic pneumonias heal without major sequelae. 

The eosinophilic pneumonias may manifest by different clinical-imaging syndromes, namely Loffler syndrome, chronic eosinophilic pneumonia, or acute eosinophilic pneumonia, the diagnosis of which requires both characteristic clinical-radiological features and the demonstration of eosinophilia at BAL—or on histopathology—with or without peripheral blood eosinophilia. 

BAL is a good noninvasive surrogate of lung biopsy for the diagnosis of eosinophilic pneumonias, and surgical lung biopsy is rarely necessary, although 

When present and associated with typical clinical-imaging features, markedly elevated peripheral blood eosinophilia ( 1 x 10 eosinophils/L and preferably 1.5 x 10 eosinophils/L) contributes to the diagnosis of eosinophilic syndromes and may obviate the need for BAL, although it does not prove that the observed pulmonary opacities correspond to eosinophilic pneumonia. Peripheral blood eosinophilia rapidly drops to normal upon corticosteroid treatment. It is often absent at presentation in lAEP. 

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