Hypereosinophilic Syndrome (Idiopathic Hypereosinophilic Syndrome) By Jane Liesveld, MD, James P Wilmot Cancer Institute, University of Rochester Medical Center Reviewed / Revised Feb 2022 | Modified Sep 2022 View Patient Education Symptoms and Signs Diagnosis Prognosis Treatment Key Points Topic Resources Clonal Hypereosinophilic... Abnormalities in Patients... Hypereosinophilic syndrome is a condition characterized by peripheral blood eosinophilia with manifestations of organ system involvement or dysfunction directly related to eosinophilia in the absence of parasitic, allergic, or other secondary causes of eosinophilia.