Idiopathic hypereosinophilic syndrome presenting with eosinophilic pleural and pericardial effusions: A case report

Hypereosinophilic syndrome (HES) is a rare disorder characterized by persistent eosinophilia and multi-organ involvement, often mimicking common conditions. We report a 36-year-old male with fever, cough, and pleuritic chest pain, initially diagnosed with community-acquired pneumonia. His condition deteriorated despite antibiotic therapy, leading to further evaluation revealing marked peripheral eosinophilia (3.79 × 10⁹/L) and eosinophilic pleural effusions. Extensive workup excluded secondary causes, leading to a diagnosis of idiopathic HES. The patient responded rapidly to corticosteroid therapy, with clinical and radiological improvement. This case highlights the importance of considering HES in patients with unexplained eosinophilic effusions and the role of early corticosteroid intervention in management. • Rare presentation of idiopathic hypereosinophilic syndrome (HES) with eosinophilic pleural and pericardial effusions. • Initially misdiagnosed as community-acquired pneumonia due to overlapping clinical features. • Comprehensive diagnostic workup ruled out secondary causes, confirming idiopathic HES. • Rapid clinical and radiological improvement achieved with corticosteroid therapy. • Emphasizes the importance of considering HES in unexplained eosinophilic effusions.