METHODS: This is retrospective review of two patients with idiopathic HES (both negative for FIP1L1-PDGFRA and workup for other forms of HES) who responded to mepolizumab.
Patient #1: 57 yo female with iHES with pruritic rash and cardiac involvement complicated by troponin leak, cardiogenic shock, cardioembolic CVA from mural thrombus initially presented with 5,990 eosinophils/mm3. She refused hydroxyurea and remained on steroids for about 2.5 years with frequent recurrence of skin involvement when steroid dose was reduced below 10 mg. After significant weight gain, LFTs became abnormal and fatty liver disease was diagnosed. Off-label coverage of mepolizumab 100 mg q 4 weeks was approved. Since starting mepolizumab 6 months ago, her eosinophil count decreased to zero and so far, prednisone has been weaned to 5 mg daily with normalization of LFTs, maintenance of disease control and desired 22 pound weight loss.
Patient #2: 45 yo female with iHES with pruritic skin involvement and angioedema who presented with 1,746 eosinophils/mm3. She was dependent on prednisone 9 mg daily for about 2 years prior to starting mepolizumab. Since starting mepolizumab 16 months ago, her eosinophil counts have been zero and she successfully tapered off prednisone 12 months ago without any recurrence of her skin involvement and some desired loss of weight.
CONCLUSIONS: Consistent with prior published work, mepolizumab may be an effective steroid-sparing agent for some patients with iHES.