Introduction Hypereosinophilic syndromes are characterized by the sustained overproduction of eosinophils, which can infiltrate various organs and release toxins that damage tissues. Causes of increased eosinophils include 1) primary or neoplastic causes (e.g., stem cell, myeloid, or eosinophil neoplasia, and clonal disorders); 2) secondary or reactive causes (e.g., parasitic infections, solid tumors, and T-cell lymphomas); 3) idiopathic causes: part of specific syndromes (e.g., Churg-Strauss); and 4) hypereosinophilia of unknown significance, when there is no organic damage. When specifically discussing rheumatic […]