The definition of eosinophilic pneumonia depends on clinical context. In pathology, eosinophilic pneumonia refers to a histologic pattern of diffuse pulmonary infiltrates that contain prominent numbers of eosinophils. Distinguishing the histologic pattern of eosinophilic pneumonia from clinical syndromes that also contain the term eosinophilic pneumonia (eg, chronic eosinophilic pneumonia, tropical pulmonary eosinophilia, simple eosinophilic pneumonia, acute eosinophilic pneumonia) is important.
Histologic areas of eosinophilic pneumonia are characteristic of biopsies from patients with all these syndromes. Nonetheless, the syndromes themselves are diagnosed based on the clinical features in conjunction with other laboratory tests, including biopsies. In this context, identification of eosinophilic pneumonia in lung biopsies may be helpful in the diagnosis and classification of these syndromes when the clinical features are atypical. Biopsies may also provide further information of potential etiologies.
This article reviews pathologic findings, epidemiologic, etiologic, prognostic, and therapeutic aspects of eosinophilic pneumonia in the context of the major clinical pulmonary eosinophilic syndromes, which are as follows:
Chronic eosinophilic pneumonia
Acute eosinophilic pneumonia
Simple eosinophilic pneumonia
Tropical pulmonary eosinophilia
The differential diagnosis discusses disorders in which eosinophilic pneumonia often occurs as part of a spectrum of pathologic findings. These entities include the following:
Allergic bronchopulmonary aspergillosis
Pulmonary Langerhans cell histiocytosis