Background: An increasing number of cases of Moyamoya disease have been reported in the Japanese and US literature. We performed this study to quantify the rise in the prevalence of Moyamoya disease and to study the unique epidemiological and clinical features in the USA that may explain a change in incidence. Methods: We analyzed data derived from patients entered in the Nationwide Inpatient Sample between 2005 and 2008, using ICD-9 codes for Moyamoya disease. Data including patient age, gender, ethnicity, secondary diagnosis, medical complications, and hospital costs were obtained. Results: From 2005 to 2008 in the USA, there were an estimated 7,473 patients admitted with a primary or secondary diagnosis of Moyamoya disease. Patients admitted with Moyamoya disease were most frequently women and Caucasian. Overall, ischemic stroke was the most common reason for admission. Hemorrhagic stroke was more frequent in adults compared with children, 18.1 versus 1.5% (p < 0.05). Conclusion: The number of patients identified and admitted with Moyamoya disease has risen dramatically in the last decade. This study can lead to a better understanding of the disease pattern and healthcare consequences in the USA and suggests that pathophysiologic differences in Moyamoya disease may exist.

This is the first study to estimate the prevalence of Down syndrome in patients with moyamoya disease. The 26-fold-greater prevalence of Down syndrome in patients with coexisting moyamoya disease compared with the prevalence of Down syndrome among live births (145 per 100,000) highlights the need for a better understanding of the common pathophysiology of the 2 conditions.

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