A Very Rare Case of Hypereosinophilic Syndrome Secondary to Natural Killer/T-Cell Lymphoma.

Hypereosinophilic syndrome (HES) is a systemic disease characterized by an increased peripheral blood eosinophil count accompanied by systemic organ dysfunction. HES is classified into idiopathic HES, primary (neoplastic) HES (HES), and secondary (reactive) HES (HES). In this case report, a patient who developed peripheral blood eosinophilia and granulation tissue in the pharynx and paranasal sinus, which was initially diagnosed as chronic eosinophilic leukemia (CEL), categorized as HES, but was eventually identified after the patient had died as natural killer/T-cell (NK/T) lymphoma, nasal type (ENKL), categorized as HES, is presented. ENKL-induced HES is very rare but must be considered.