The term applies to patients with leukemia who at the time of diagnosis have extreme increases in their white blood cell count. This circumstance occurs most frequently in patients with chronic myelogenous leukemia. If severe enough, blood flow may be impaired by the very high concentration of immature leukocytes. Urgent treatment by hemapheresis and chemotherapy is usually administered if symptoms are severe.
Whether patients at high risk of CNS relapse (for example, age greater than or equal to10 years, presence of hyperleukocytosis, or T cell ALL) continue to require cranial radiation in addition to extended intrathecal therapy is controversial.