Abstract

*Background: Moyamoya disease (MM) is a rare disorder of the cerebral arterial circulation, while multiple sclerosis (MS) is a relatively common disorder resulting from an immune-mediated attack on central myelin. Despite the differences in pathogenesis, the two disorders share some clinical features, and this can lead to diagnostic confusion: both can affect young adults, cause intermittent neurological symptoms, and show multifocal abnormalities on brain imaging. *Goal: To emphasize the need for early consideration of MM in the differential diagnosis of MS-spectrum disorders. *Methods: Chart reviews and individual case analyses. *Results: We present detailed descriptions of three patients with MM, and summary data on eight additional patients, in which there was diagnostic confusion with MS, with delay in treatment ranging from 2 months to 19 years (median = 4 years). *Conclusion: MM can be misdiagnosed as MS, leading to delay in treatment; additionally, the treatment of these disorders is very different. We highlight the clinical and radiological features that should allow differentiation of these conditions early in their course, when treatment can have maximum benefit.