Idiopathic hypereosinophilic syndrome with 20 years of diagnostic delay

Eosinophils are specialized granulocytes that produce and store diverse biologically active molecules, including cytotoxins, cytostimulatory proteins, lipid mediators, chemotactic peptides, cytokines, leukotriens and prostaglandins.1 Eosinophils can also cause direct damage to microorganisms and can activate cells and platelets.1,2 The normal count ranges between 0.05 and 0.5 × 109/L in the peripheral blood and between 1% and 6% in a myelogram.3 Hypereosinophilia is defined as persistent eosinophilia (>1.5 × 109/L) over a minimum of four weeks.3,4 Major causes of hypereosinophilia are helminth infections, allergies, atopy and drugs, which are described as secondary hypereosinophilia due to the production of interleukin (IL)3 and IL-5 that promote eosinophil proliferation. Lymphomas, lymphoblastic leukemia, some solid tumors and some autoimmune diseases are less common causes.3–5 In primary hypereosinophilia, eosinophils are clonal and are derived from