P93 | Hypereosinophilic syndrome and novel eosinophil-depleting therapies

Premises: Hypereosinophilic syndrome (HES) is a rare systemic inflammatory disorder characterized by an elevated eosinophil count and a heterogeneous clinical presentation. Conventional treatments may have significant dose-limiting side effects, but novel therapies targeting eosinophils may offer a more favourable efficacy and safety profile, in particular, mepolizumab, a monoclonal antibody neutralizing interleukin 5 (IL-5) and commonly used at a dosage of 100 mg for treating severe asthma, has recently been approved for HES at a dosage of 300 mg every 4 weeks.Description of the Case report: An 83 yrs old patient with history of asthma and mild eosinophilia, was admitted for fatigue, arthromyalgia, and peripheral neuropathy, associated with hypereosinophilia (21.000/µL) and >20% eosinophilic infiltration in bone marrow. Extensive diagnostic tests (including bone marrow biopsy, cytogenetics, molecular testing for BCR-ABL and major rearrangements) ruled-out major organ involvement, infections, malignancies, and myeloproliferative diseases. Diagnosed with HES, the patient was treated with prednisone (25-50 mg QD), followed by subcutaneous mepolizumab (300 mg every 4 weeks), resulting in symptom resolution and prolonged steroid-sparing effects.Conclusions: IL-5 targeted therapy resulted in decreased eosinophil counts, preventing relapses within 6 months, and reducing prednisone to <5 mg QD, minimizing long-term systemic corticosteroid side effects. Mepolizumab showcased efficacy in HES, offering a promising treatment with potential long-term benefits.