Hypereosinophilic syndrome presenting as pleural and pericardial effusion in a Pediatric patient: a rare case report.

Hypereosinophilic syndrome is a rare disorder in children, particularly when presenting with simultaneous pleural and pericardial effusions. We report the case of a 4-year-old girl who presented with fever, cough, shortness of breath, and chest pain. Clinical evaluation revealed bilateral pleural effusion and later pericardial effusion with impending tamponade. Laboratory investigations showed marked hypereosinophilia, while infectious, rheumatologic, and malignant causes were excluded. Bone marrow findings confirmed eosinophilic predominance without atypia. The patient underwent pericardiocentesis and was treated with corticosteroids, resulting in clinical improvement and normalization of eosinophil counts. On follow-up, she remained asymptomatic with resolution of effusions. This case underscores the importance of considering HES as a differential diagnosis in pediatric patients with eosinophilic effusions and highlights the role of early recognition and corticosteroid therapy in preventing life-threatening complications.