D1.353 - When eosinophils surpass the limits without a known cause

The eosinophils represent about 1-5% of circulating leucocytes, with interleukin-5 (IL-5) receptors on their surface. They are important for the immune response, although its elevation may cause serious complications. Hypereosinophilia (HE) is defined as an absolute eosinophil count >1500 cells/uL in peripheral blood. Hypereosinophilic syndrome (HES) occurs in the presence of eosinophil-mediated organ damage.

We report a Portuguese female patient, 72 years-old (yo), who worked at a gardening center. At the age of 66 yo the patient presented with generalized pruritus, xerosis, erythema and scaling skin of the back, neck, scalp, hands and retro-auricular area and fatigue. Blood analysis revealed sustained hypereosinophilia and markedly elevated total serum IgE. Biochemical tests were unremarkable. Triptase was in the normal range, negative autoimmunity workup. Skin biopsy revealed perivascular lymphocytic infiltrate with eosinophils. Exhaustive search for parasitological infection was performed. Prick tests were negative as also epicutaneous tests that included fitoalergens batteries and specific plants used in her professional activity. Head, thoracic and abdominal CT, as well as echocardiogram and functional respiratory studies were normal. Myelogram and bone marrow biopsy revealed no alterations. FIP1L1 and TELPDGFRb mutations were not detected in peripheral blood and bone marrow, excluding primary HES. The diagnostic of idiopathic HES was assumed, and steroids were started, with clinical and hematologic improvement. Adverse effects limited long-term management. A trial with azathioprine was made, but tolerance was limited and treatment interrupted after alopecia and visual disturbances developed. The patient started monthly mepolizumab, with progressive improvement and after five months of treatment, there was a significant and consistent reduction of eosinophilia without adverse effects, even after removal of corticotherapy.  

Idiopathic HES is a rare condition characterized by sustained eosinophilia in peripheral blood, associated with organ damage, that requires a thorough exclusion of primary and secondary causes. This clinical report highlights the challenges in the diagnosis of HES and its long-term management. Systemic corticotherapy is the first line treatment, but has many adverse effects. Mepolizumab, an anti-IL-5 monoclonal antibody, appears to be an effective and safe alternative in managing refractory cases.