leukostasis

Leukostasis is a medical emergency defined by symptomatic hyperleukocytosis with microvascular occlusion caused by markedly elevated circulating leukemic blasts. It most often occurs in acute leukemias, particularly acute myeloid leukemia, but can also be seen in acute lymphoblastic leukemia and, less commonly, chronic myeloid leukemia in blast crisis. The condition results from increased blood viscosity and direct adherence of blasts to endothelium, leading to impaired microcirculatory flow in the brain, lungs, and other organs.

Clinical features reflect the organs involved. Neurologic symptoms include headache, confusion, dizziness, visual changes, and, in some cases, focal deficits or coma. Respiratory involvement can cause dyspnea and hypoxemia due to pulmonary microvascular sludging. Other manifestations may include chest pain, hypoperfusion signs, renal impairment, or rarely priapism.

Diagnosis relies on rapid assessment in the setting of severe leukocytosis, with peripheral smear showing a high proportion of blasts and a markedly elevated white blood cell count. Imaging and organ-specific studies are guided by symptoms. It is distinct from a leukemoid reaction, as leukostasis specifically involves leukemic blasts and microvascular occlusion rather than benign neutrophilia.

Treatment is urgent and multifaceted. Immediate cytoreductive therapy to reduce blast counts is essential, typically with leukapheresis to rapidly decrease circulating blasts, followed by systemic chemotherapy appropriate to the underlying leukemia. Hydroxyurea may be used for rapid cytoreduction in some cases. Supportive care includes oxygenation, hydration, management of electrolyte disturbances and tumor lysis syndrome, infection prevention, and careful transfusion decisions. Early recognition and prompt intervention improve outcomes, but leukostasis carries a high risk of mortality if not promptly treated.