Introduction

Acute eosinophilic pneumonia (AEP) is one of a heterogeneous group of disorders collectively termed the eosinophilic pneumonias or eosinophilic lung diseases. These disorders are characterized by eosinophilic infiltration of the lung, which may or may not be accompanied by peripheral blood eosinophilia. Eosinophilic pneumonia may be seen in association with a diverse group of known clinical disorders including parasitic and fungal infections, immunologic and systemic diseases, and drug toxicity. These secondary forms can present as simple, acute, or chronic eosinophilic pneumonia. In the absence of an identifiable cause, simple, acute, and chronic eosinophilic pneumonia may also be idiopathic.

Eosinophilic lung disease can be diagnosed by several means. Infiltrates on chest radiographs combined with peripheral blood eosinophilia can be used to define eosinophilic pneumonia, however, this indirect approach has two limitations. First, peripheral blood eosinophilia does not prove infiltrates on chest radiographs are eosinophilic in origin, and second, eosinophilic infiltration of the lung is not always accompanied by peripheral blood eosinophilia. More directly, pulmonary eosinophilia can be assessed using bronchoalveolar lavage (BAL) or lung biopsy (open or transbronchial).