Idiopathic Hypereosinophilic Syndrome Presenting As Eosinophilic Ascites and Pleural Effusion in an Elderly Male: A Rare Clinical Manifestation

Hypereosinophilic syndrome (HES) is a rare disorder marked by sustained blood eosinophilia and associated tissue or organ damage in the absence of a secondary identifiable cause. Eosinophilic ascites and pleural effusion are extremely rare clinical presentations of idiopathic HES and often mimic malignancy, tuberculosis, or parasitic infections. We report a case of idiopathic HES in a 68-year-old male presenting with exudative eosinophilic ascites and pleural effusion. Extensive workup, including histopathology and bone marrow evaluation, confirmed the diagnosis. He responded favorably to corticosteroid therapy. This case highlights the importance of considering idiopathic HES in patients with eosinophilic effusions when common etiologies are excluded.