White matter hyperintensity burden in elderly cohort studies: The Sunnybrook Dementia Study, Alzheimer's Disease Neuroimaging Initiative, and Three-City Study.

Given the recent acknowledgement of the complex mixed pathologies that contribute to the clinical expression of dementia, various cohort studies have aimed to examine Alzheimer's disease and cerebrovascular disease as comorbid pathologies, with neuroimaging playing a central role in these studies. Using white matter hyperintensities (WMH) as a biomarker of cerebrovascular disease, we compared WMH burden between the Sunnybrook Dementia Study, the Alzheimer's Disease Neuroimaging Initiative (ADNI-1), the Three-City Study, and various other studies around the world. Based on our findings, it was evident that ADNI-1 had minimal WMH burden relative to other large studies that examine aging and dementia. This low WMH burden in ADNI-1 may be considered as both an advantage, representing a relatively "pure" sample with little confounding vasculopathy, and a disadvantage, as it limits generalizability to "real-world" patient populations with mixed pathologies and to nondemented groups with baseline vascular disease. We explore possible reasons for this distinction, including management of vascular risk factors, gaps in diagnostic criteria, and future directions for clinical research.