Evaluation and Treatment of a Severe Case of Pediatric Idiopathic Hypereosinophilic Syndrome

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BackgroundHypereosinophilic syndromes (HES) are a group of rare disorders characterized by marked peripheral eosinophilia resulting in end organ damage. When evaluating a patient with persistent hypereosinophilia, it is important to screen for the more common secondary causes of eosinophilia and assess for primary, myeloid HES. When no clear etiology is determined, a diagnosis of idiopathic HES is made. While this evaluation can be clinically challenging, making an accurate diagnosis can help guide effective treatment. CaseA 3-year-old Caucasian female with profound peripheral eosinophilia (70,100 cells/mL) and lymphocytosis (24,900 cells/mL) presented for immunologic evaluation following a two year history of persistent eosinophilia (1,450–27,700 cells/mL), presumably secondary to recurrent toxocariasis. The patient had been treated with albendazole three times for Toxocara after having positive serology and imaging consistent with visceral larva migrans in the context of an otherwise negative extensive infectious evaluation. Intermittent oral steroids and daily medium-dose inhaled steroids had also been started for wheezing. A bone marrow biopsy (BMbx) demonstrated increased numbers of eosinophils with cytoplasmic vacuoles, areas of hypogranulation, and subtle segmentation abnormalities, but genetic rearrangements for PDGFRA, PDGFRB, FIP1L1, and JAK2 were negative. An abnormal population of lymphocytes (CD3-CD4+) making up 1.7% of total lymphocytes was noted; however, this was not reproducible on repeat BMbx. Positron emission tomography redemonstrated bilateral pulmonary nodules and mild hilar lymphadenopathy, and bronchoalveolar lavage was normal other than an eosinophilia. The remainder of her immunologic evaluation was normal other than a pan-hypergammaglobulinemia without evidence ofT or B cell clonality. A 429 gene primary immunodeficiency panel was not felt to be clinically significant.Given the patient's persistent eosinophilia, oral steroids at 2 mg/kg were started with only a partial response (2,600 eosinophils/mL). Ultimately, mepolizumab 100 mg injected subcutaneously every 4 weeks was started as steroid sparing therapy with an excellent clinical response (780 eosinophils/mL) even after weaning off of oral steroids. ConclusionThis unique case illustrates the importance of a thorough evaluation of patients with persistent eosinophilia and the efficacy of mepolizumab in a child with marked idiopathic HES.