TREATMENT OF HYPEREOSINOPHILIA WITH MEPOLIZUMAB IN A 6-YEAR-OLD BOY

Abstract

<h3>Introduction</h3> Hypereosinophilic syndrome (HES) is a rare cause of hypereosinophilia among pediatric patients. Mepolizumab, an IL-5 antagonist, is an effective treatment for hypereosinophilia approved for patients ≥12 years of age, but for younger children treatment remains limited to corticosteroids or other cytoreductive agents. This case illustrates successful treatment of hypereosinophilia with mepolizumab in a child. <h3>Case Description</h3> A previously heathy 6-year-old male presented with three days of fatigue, fever, and right cervical lymphadenopathy with an elevated absolute eosinophil count (AEC) that peaked at 83,350 cells/microliter. Work up for infectious disease, end-organ damage, and malignancy with flow cytometry and cytogenetics from blood, bone marrow and lymph node biopsy were negative. Mepolizumab 100 mg injected subcutaneously was given, leading to progressive decline in AEC to 3,370 cells/microliter after 14 days. Fevers, fatigue, and lymphadenopathy resolved. Monthly mepolizumab and close monitoring is planned. <h3>Discussion</h3> HES is a heterogenous group of disorders; of paramount concern is development of malignancy and end-organ damage due to eosinophilic infiltration of tissues. Although effective for hypereosinophilia, long-term treatment with corticosteroids is associated with significant adverse events and may cause diagnostic uncertainty when monitoring pre-malignant conditions. While mepolizumab is approved for children ≥6 years of age for the treatment of asthma, it is not approved for HES in this age group. This case highlights that mepolizumab is an effective steroid-sparing therapy in young children with hypereosinophilia that allows continued monitoring for malignancy without masking or delaying diagnosis from corticosteroid use.