C48-29 Unmasking the Mimic: A Case of Idiopathic Acute Eosinophilic Pneumonia in Undifferentiated Respiratory Failure

Abstract Introduction Acute eosinophilic pneumonia (AEP) was first described in 1984 as an idiopathic febrile respiratory illness with eosinophilic infiltration (25%) on broncho-alveolar lavage and diffuse parenchymal infiltrates on imaging. While the idiopathic form (IAEP) has become progressively uncommon as a growing list of environmental and pharmacological triggers is identified, AEP remains a vital diagnostic consideration in cases of acute respiratory distress syndrome (ARDS), as it often mimics its presentation. Here we present a patient admitted to the intensive care unit with respiratory failure and fever, highlighting the importance of exposure history and consideration of early bronchoscopy for the diagnosis of AEP. Case Presentation A 31-year-old female without smoking history or known lung disease was admitted with 4 days of progressive dyspnea, chest pain, and fever. Examination revealed tachycardia, tachypnea, and hypoxia requiring noninvasive mechanical ventilation with 60l/100% high flow nasal cannula. Labs were notable for leukocytosis (19K) alone, and unremarkable for peripheral eosinophilia, autoimmune panel, and extensive infective workup including for parasites. Chest imaging was notable for bilateral lower lobe predominant diffuse areas of ground glass opacities and patchy consolidation. Exposure history included recent travel to upstate New York where she swam in the lakes, a friend with shingles, and increased use of heavy metal concentrations at her job an alloy mixing dosimetrist. Despite broad spectrum antibiotics and diuresis, she remained persistently febrile and hypoxic for 3 days. Bedside bronchoscopy with lavage revealed eosinophilia (50%) and no infection. She was started on high dose steroids, weaned off supplemental oxygen and discharged home within 10 days of presentation. Discussion Although less than 500 cases have been reported in literature, AEP is an important mimicker of acute respiratory distress syndrome and warrants consideration as an important differential in the management of respiratory failure. This patient represents a case of IAEP with acute onset respiratory failure, prominent pulmonary eosinophilia on BAL, and dramatic improvement with steroids in the absence of known AEP triggers or systemic eosinophilic conditions. This outcome highlights that AEP, even in the presumed absence of known triggers (IAEP), is remarkably sensitive to steroid therapy. Additionally, when presented with undifferentiated respiratory failure with persistent fever, this case highlights the importance of performing bronchoscopy with BAL early in the hospital stay, to aid in ruling out mimickers of ARDS. This abstract is funded by: None