More Than Five Years of Sustained Remission With Mepolizumab in Adolescent-Onset Eosinophilic Granulomatosis With Polyangiitis: A Case Report.

Eosinophilic granulomatosis with polyangiitis (EGPA) typically affects middle-aged adults, and adolescent-onset disease is rare and scarcely documented in long-term real-world follow-up. We describe an 18-year-old woman with asthma who presented with fever, muscle pain, wet cough, and dyspnea. Laboratory tests showed marked leukocytosis (27,600/µL) with severe eosinophilia (17,940/µL), elevated creatine kinase, normal Krebs von den Lungen-6, elevated surfactant protein-D, markedly elevated serum immunoglobulin E, and negative proteinase 3- and myeloperoxidase-anti-neutrophil cytoplasmic antibody. Imaging revealed bilateral patchy infiltrates, and transbronchial lung biopsy demonstrated eosinophilic infiltration with granuloma formation and features of vasculitis, establishing the diagnosis of EGPA. Prednisolone 25 mg/day induced rapid improvement with normalization of eosinophils by day 12. She remained stable for nearly two years on low-dose prednisolone until asymptomatic eosinophilia recurred during tapering. Mepolizumab 300 mg every four weeks was then initiated, leading to immediate eosinophil normalization. Prednisolone was discontinued three years and 10 months after starting mepolizumab, and she has maintained remission for more than five years under continued therapy. This real-world case shows that, in adolescent-onset EGPA, where corticosteroids alone controlled disease for only two years, mepolizumab achieved sustained remission without significant adverse effects and enabled complete steroid withdrawal, underscoring its value as a long-term steroid-sparing strategy.