Adam de Havenon, MD

Rostamian S, Mahinrad S, Stijnen T, Sabayan B, and de Craen AJM. Cognitive Impairment and Risk of Stroke: A Systematic Review and Meta-Analysis of Prospective Cohort Studies. Stroke. 2014

Dementia and cognitive impairment are well associated with prior stroke and white matter lesion burden. Less well established is the future risk of stroke for patients with cognitive impairment, but no vascular history. A guiding principle in the quest to find effective treatment for dementia is to identify patients at risk of developing dementia and treating them preemptively with established therapeutics or enrolling them jn research trials.

Somayeh Rostamian et al.’s meta-analysis looked at 12 studies that tested cognitive function and followed patients to see if they had stroke. The vast majority of the 82,899 patients had no history of stroke and during the 3 to 21 years of follow-up there were 3043 stroke events (3.7%). The meta-analysis controlled for traditional vascular risk factors. The RR for stroke was 1.19 for every downward standard deviation in global cognitive performance, with insignificant differences in RR if the impairment was executive function, attention, memory, or language function.
The studies included in this meta-anlaysis have several limitations, the most vexing being that only one study reported MRI data, which was limited to structural morphology and a white matter hyperintensity score, making it difficult to exclude patients with mild cognitive impairment from subclinical strokes. Only 3 studies did repeat cognitive testing and without longitudinal data, it is difficult to ascertain if the incident strokes were significant from a cognitive perspective. Ultimately, physicians evaluating a patient with new cognitive impairment should always consider nascent vascular dementia and multiple guidelines, including the AAN guidelines, specify just that and call for structural brain imaging at diagnosis. As such, the association reported in this study seems low yield, both for its limited novelty and low RR.