Case Presentation: 65-year-old female with a past medical history of hypertension and colonic diverticulosis presented to emergency department with progressively worsening dyspnea for two months. This was associated with orthopnoea and wet cough. Before presentation, she completed a course of Levofloxacin and steroids in an outpatient clinic. On examination, she was hypoxic with basilar crackles and pedal edema. Blood count revealed leukocytosis of 12.4 K/uL and absolute eosinophil count (AEC) of 3.9 K/uL. Chest radiography revealed bilateral pleural effusion, interstitial edema, and left lower lobe consolidation. Intravenous diuretics and antibiotics were initiated. Echocardiography revealed hypertrophic left ventricular basal septum with grade 1 left ventricular diastolic dysfunction with ejection fraction 65 – 69%. Therapeutic thoracocentesis was performed, and pleural fluid analysis revealed exudative effusion with abundant eosinophils. She was not on medications with eosinophilic potential. Parapneumonic effusion, hypertrophic cardiomyopathy, and malignancy were the differentials. Computerized tomography ruled out lung and pleural lesions. Cardiac magnetic resonance imaging ruled out myocardial infiltration. Eventually, her symptoms moderately improved, and she was discharged with supplemental oxygen and diuretics, with plan for outpatient evaluation.Within a week after discharge, she was readmitted for acute hypoxic respiratory failure. Blood count showed AEC > 7.8 K/uL. Chest radiography showed moderate bilateral pleural effusion. Intravenous corticosteroids were initiated. Longitudinal lab review revealed persistent eosinophilia over two months, which prompted further evaluation for the hypereosinophilic syndrome (HES). IgE was elevated >1400 kU/L. Tryptase levels were normal. Peripheral smear revealed eosinophilia, spherocytes, and atypical lymphocytes. Serum protein electrophoresis, immunofixation, and flow cytometry were unremarkable. Fluorescence in situ hybridization was negative for BCR-ABL, platelet-derived growth factor receptor α/β, and fibroblast growth factor receptor. Parasitic and viral infection and autoimmune workup were unremarkable. Bone marrow biopsy revealed hypercellular bone marrow with eosinophilia. Idiopathic-acquired HES was diagnosed by exclusion. After initiating steroids, symptoms rapidly improved with a rapid decline in AEC to 0.24 K/uL. She was discharged on prednisone.

Discussion: HES is a rare disorder characterized by chronic peripheral blood hypereosinophilia 1.5 K/uL, with end-organ involvement and lack of evidence of other causes of eosinophilia. Eosinophilic pleural effusion (EPE) comprises of 7.3% of all effusions and is a rare manifestation of HES.(1,2) Pleural effusions in HES are attributed to heart failure due to eosinophilic myocarditis. Our patient was initially treated for pneumonia and heart failure until cardiac infiltration was ruled out. It is crucial to eliminate common causes of EPE, like infection, autoimmune disorders, and malignancies. Myeloproliferative panel and bone marrow biopsy help differentiate the subtypes – lymphocytic, myeloid, and idiopathic. (3) Idiopathic HES is a diagnosis of exclusion and responds well to corticosteroids.

Conclusions: Through this case, we discuss the systematic evaluation of HES. Although rare, idiopathic acquired HES in immunocompetent patients must be considered a differential in patients presenting with EPE and timely management is essential.