INTRODUCTION: Idiopathic Acute Eosinophilic Pneumonia (IAEP) is a rare cause of acute respiratory failure, with unknown pathogenesis. The authors present one of the most severe reported cases of IAEP, in a young smoker, and the first reported successful use of Extracorporeal Membrane Oxygenation (ECMO) for IAEP in an adult patient.
CASE PRESENTATION: A 20 year old previously healthy Caucasian woman, who started smoking tobacco cigarettes two weeks ago, presented with acute onset of fever, dyspnea and productive cough. She was febrile and hypoxemic, with bilateral diffuse ronchi on chest auscultation. She had leukocytosis of 28.5 k/µL, with neutrophilia. Diffuse bilateral alveolar infiltrates were seen on chest radiograph and CT scan. Broad spectrum intravenous antibiotics were initiated for presumed community acquired bacterial pneumonia. She required invasive mechanical ventilation within 6 hours of admission, and her hypoxemia continued to worsen. An arterial blood gas (ABG), on 100% FIO2 and positive end expiratory pressure of 20 cmH2O on mechanical ventilation, revealed a normal pH and PCO2, with a PaO2 of 50 mmHg. Therefore, veno-venous ECMO was initiated, with 100% FIO2, and sweep gas flow of 6 Liters/ minute. A subsequent ABG showed a PaO2 of 70 mmHg. Blood, urine and stool cultures were negative. Bronchoalveolar lavage (BAL) showed marked eosinophilia of 43%, and no pathogenic bacteria, mycobacteria, fungi or viruses. ANA and ANCA were not detected. The patient was diagnosed with IAEP. Intravenous methylprednisolone was initiated at 60 mg every 8 hours, until she was weaned from ECMO and mechanical ventilation 48 hours later, followed by transition to oral prednisone, which was tapered over eight weeks. She had complete resolution of disease when discharged on the tenth day of hospitalization, with no evidence of recurrence 16 weeks later.
DISCUSSION: First described in 1989, roughly 150 cases of IAEP have been reported worldwide. The diagnostic criteria consists of an acute febrile illness with respiratory failure, diffuse bilateral alveolar or interstitial lung infiltrates on chest radiograph and eosinophilia of 25% or greater in BAL fluid, in the absence of infection or alternative cause for eosinophilia 1. IAEP falls under the heterogeneous group of eosinophilic lung diseases and should be distinguished from clinically similar entities. In our patient, drug, toxin and animal exposure, an infectious etiology and connective tissue disease were excluded. Allergic bronchopulmonary aspergillosis was unlikely given the lack of history for asthma. Although the exact pathophysiology is unknown, IAEP is thought to be caused by acute hypersensitivity to inhaled allergens. Certain inflammatory mediators, particularly interleukin-5, are elevated and have been shown to signal eosinophilic activation and migration 1. Many reported cases appear to be associated with recent smoking, including our patient. However, no direct pathway has been found between cigarette smoke and interleukin activation. Other implicated toxins include tear gas, gasoline, and cocaine 1. Corticosteroid treatment results in a dramatic improvement in symptoms within 48 hours 1. Long term prognosis is excellent, with no reported recurrence. The challenge, however, lies in timely diagnosis and treatment, since IAEP may resemble acute lung injury or acute infectious pneumonia, as in our patient. This is the only reported case of IAEP in an adult patient, where ECMO was used successfully to manage respiratory failure while further diagnostic testing was underway and the therapeutic effect of corticosteroids was awaited.
CONCLUSIONS: IAEP is a rare disease of unclear pathophysiology. Tobacco smoking may be associated with some cases, including our patient. IAEP can cause severe acute respiratory failure, which may be managed successfully with ECMO, while measures are taken to establish a definitive diagnosis and treatment.
Reference #1 Philit F. et al. Idiopathic Acute Eosinophilic Pneumonia: A Study of 22 Patients. Am J Respir Crit Care Med, 2002; 166:1235-1239
DISCLOSURE: The following authors have nothing to disclose: Maryam Gul, Robert Freed, Nida Rizvi, Margaret Wojnar
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