Moyamoya Syndrome in Patients With Down Syndrome and Acute Lymphoblastic Leukemia.

Moyamoya syndrome (MMS) is a chronic vasculopathy characterized by progressive stenosis of intracerebral arteries, leading to an increased risk of stroke. Children with Down syndrome (DS) are at an increased risk of co-occurring medical conditions, including MMS and leukemia. We report four patients with the triad of DS, MMS, and acute lymphoblastic leukemia (ALL). Two patients had a diagnosis of MMS prior to developing ALL, whereas two were diagnosed with MMS during ALL therapy. This series highlights the need to remain cognizant of MMS in patients with DS and ALL, particularly in those with acute neurologic changes.