Hypereosinophilic syndrome evolving to acute lymphoblastic leukemia

We report a case of hypereosinophilic syndrome (HES) which later evolved into acute lymphoblastic leukemia (ALL). A 37-year-old man showed typical clinical manifestations of HES: pulmonary infiltrates, erythematous skin rash, deep vein thrombosis, endomyocardial fibrosis, and diffuse central nervous system dysfunctions. Although he was treated with prednisolone and hydroxyurea, marked eosinophilia persisted and lymphoblasts gradually increased in the bone marrow. He died of severe disseminated fungal infection after anti-leukemic therapy. Autopsy revealed marked fibrous thickening of the endocardium, bilateral common iliac vein thrombosis, and chronic hepatitis with fibrosis. Neither eosinophilic nor leukemic cell infiltration was seen in any tissue at autopsy. Including this case, 24 patients with ALL and hypereosinophilia have been reported in English-language literature. We discuss the relationship between eosinophilia and ALL, and the mechanisms, particularly the role of eosinophil cationic protein (ECP), in causing various organ system dysfunctions in HES.