Idiopathic acute eosinophilic pneumonia: A retrospective case series and review of the literature

Introduction: Idiopathic acute eosinophilic pneumonia (AEP) is characterized by hypoxemia, pulmonary infiltrates and pulmonary eosinophilia. Data is limited and the purpose of this study is to better understand this disorder. Methods: A search of the computerized patient records from January 1, 1997 to October 15, 2010 for patients with suspicion of "eosinophilic pneumonia" was conducted. Included patients were 18 years or older with an acute febrile illness, hypoxemia, diffuse pulmonary infiltrates on imaging, and pulmonary eosinophilia. Patients were excluded with other known causes of pulmonary eosinophilia. Results: Of 195 patients with pulmonary eosinophilia, 8 patients had "definite" or "probable" and 4 patients had "possible" idiopathic AEP. Three patients were categorized as "probable" idiopathic AEP due to exceeding expected maximal 30-day symptom duration and/or a maximal recorded temperature less than 38°C. Four patients were defined as "possible" idiopathic AEP given histories of polymyalgia rheumatica, eczema or allergic rhinitis. Of the 8 included patients, 63% were male with a median age of 53. Median duration of symptoms was 21 days. Median nadir oxygen saturation was 83%. Median eosinophil count on bronchoalveolar lavage was 36%. Two patients required intubation. Two patients were current smokers, one of whom had reported a change in smoking habits. All patients were treated with steroids (median of two months). Conclusions: As diagnostic methods and pharmacologic knowledge improve, the number of patients meeting criteria for idiopathic AEP remains small. Much remains to be learned about this truly rare condition, and current criteria may exclude milder presentations of the disease.