Clinical Presentation

Patients with AEP typically present with an acute respiratory illness of 1 to 7 days duration, manifest by fever, dyspnea, cough, pleuritic chest pain, myalgias, crackles on chest auscultation, hypoxemic respiratory insufficiency, bilateral diffuse infiltrates on chest radiographs, and increased eosinophils in BAL fluid or lung biopsy. Respiratory insufficiency progresses to respiratory failure requiring mechanical ventilation in a high percentage of cases. Peripheral blood eosinophil counts may be normal, however, 19 of 27 (70%) patients described in separate studies by Umeki and Philit had peripheral blood eosinophilia greater than 0.5 x 10⁹ L at some point during the course of illness. Thus, the presence or absence of peripheral blood eosinophilia is of questionable value in recognizing AEP. Patients show a rapid response to corticosteroids, and do not relapse once corticosteroids are discontinued. Spontaneous recovery also occurs.

AEP may be mistaken for other diseases, particularly community-acquired pneumonia, resulting in delayed or missed diagnosis. As defined by the North American-European Consensus Committee, many patients with AEP meet the criteria for acute lung injury (ALI), including its most severe subset - acute respiratory distress syndrome (ARDS). Distinguishing AEP and ARDS is critical because of differences in response to corticosteroids and outcome. Although both present with rapidly progressive respiratory failure, patients with AEP characteristically show a rapid response to corticosteroids and have an excellent prognosis resulting in a favorable outcome in most patients, whereas patients with ARDS do not benefit from corticosteroid therapy and have a poor prognosis with mortality rates reported to range from 10% to 90%.