Résumé
Hyperleukocytosis (HL), defined by a peripheral white blood cell (WBC) count exceeding 100,000/mm³, is occasionally observed in childhood acute leukemia. The increased viscosity in the micro-circulation by HL and the interaction between the leukemic blasts and endometrium of blood vessels sometimes result in leukostasis. Leukostasis can incur life-threatening manifestations, such as respiratory distress, brain infarction and hemorrhage, and renal failure, needing an emergency care. Although early stage of leukostasis is difficult to detect due to nonspecific manifestations, an emergency care is mandatory because leukostasis can proceed to a fatal course. Initial management includes an aggressive fluid therapy that can reduce WBC count, and prevent other metabolic complications implicated by HL. Packed red blood cells should be judiciously transfused because it increases blood viscosity. Conversely, transfusion of platelet concentrates or fresh frozen plasma, which does not affect blood viscosity, is recommended for prevention of hemorrhage. To reduce tumor burden, leukapheresis or exchange transfusion is commonly performed. However, the efficacy is still controversial, and technical problems are present. Leukapheresis or exchange transfusion is recommended if WBC count is 200,000–300,000/mm³ or more, especially in acute myelocytic leukemia, or manifestations of leukostasis are present. In addition, early chemotherapy is the definite treatment of leukostasis.