Efficacy of hydroxyurea in a hypereosinophilic syndrome patient with significant eosinophilia

Abstract

Here, we report the case of a 14-year-old female, who presented with a headache and severe hypereosinophilia (269×10³/μL). Fluorescence in situ hybridization analysis showed she was negative for the FIPIL1-PDGFRα fusion gene, FDGFRβ, and FGFR1. Molecular testing of the patient’s bone marrow showed no evidence of T-cell receptor rearrangement. Therefore, she was diagnosed as having hypereosinophilic syndrome. Although she was initially treated with prednisolone (PSL), hydroxyurea (HU) was added as a second-line treatment, as her condition was unchanged. Upon the initiation of HU, the patient’s eosinophil count improved markedly. HU was discontinued after four months of treatment. The patient’s eosinophil count remained normal for 1 year since the end of the therapy. Our patient exhibited an immediate marked response to HU and did not suffer organ failure. However, there are no guidelines about the tapering and cessation of HU, and it is considered that careful observation and the accumulation of cases are necessary.