Cognition and white matter lesions.

Although it is recognized that ischemic stroke is a potent risk factor for vascular dementia, the influence of white matter lesions (WML) on cognitive function is less clear. In community-based MRI studies that have administered mental status tests to subjects who were free of clinically evident neurologic disease, a weak relationship between WML and generalized cognitive function has been reported. In studies that have administered neuropsychological test batteries, a stronger and more specific association has been recognized between WML and deficits in executive function, most likely due to the involvement of frontal-subcortical pathways. Cognitive deficits may be related to the total volume of the WML, with a threshold perhaps needing to be surpassed before such deficits are evident, but it is likely that the location of the WML also plays a role, with that threshold varying in association with the distribution of the lesions. Potential confounders of the results of previous studies include small, strategically located subcortical infarctions that may be masked by more extensive WML and other comorbid neurologic disorders, particularly Alzheimer's disease. Future studies should be prospective, utilize standardized methods for structural and functional brain imaging, and administer comprehensive neuropsychological assessments in order to more rigorously investigate the relationship between evolving WML and declining cognitive functions.