One-and-a-half syndrome is a clinical disorder featuring extraocular movements 
characterized by horizontal conjugate gaze palsy with internuclear 
ophthalmoplegia. It usually results from a unilateral lesion of the midbrain, 
and the most common cause of this syndrome in young women is multiple sclerosis. 
We report the case of a 38-year-old woman diagnosed as having acute myeloblastic 
leukemia presenting with characteristic neurologic and imaging features of 
one-and-a-half syndrome. Hyperleukocytosis, cancer procoagulants, tissue factor 
expression, and the increased proteolysis of coagulation factors by leukemic 
cells may all contribute to the propensity for thrombotic vascular occlusion. 
The optimal treatment of acute brain infarction in acute leukemia patients with 
hyperleukocytosis remains unclear. However, this patient illustrates that 
leukapheresis alone can provide rapid and effective relief of visual symptoms 
without neurologic sequela. To achieve better outcomes and survival, clinicians 
must maintain a heightened awareness of this distinctly unusual manifestation.