Rajbeer Singh Sangha, MD

Levine DA, Kabeto M, Langa KM, Lisabeth LD, Rogers MAM, and Galecki AT. Does Stroke Contribute to Racial Differences in Cognitive Decline? Stroke. 2015

The authors of this study tackle the interesting topic of racial disparities in dementia due to the fact that older non-Hispanic blacks have greater risk (approximately 2x) of having cognitive decline, including Alzheimer’s disease and vascular dementia, than older non-Hispanic whites. They investigated whether racial differences in cognitive decline are explained by differences in the frequency or impact of incident stroke between blacks and whites, controlling for baseline cognition. 

The study analyzed 4,908 black and white participants aged 65 and above free of stroke and cognitive impairment. They examined longitudinal changes in global cognition by race, before and after adjusting for time-dependent incident stroke followed by a race-by-incident strokes. They identified 34 of 453 (7.5%) blacks and 300 of 4,455 (6.7%) whites with incident stroke over a mean (SD) of 4.1 (1.9) years of follow-up (P=0.53). Blacks had greater cognitive decline than whites and even with further adjustment for cumulative incidence of stroke, the black-white difference in cognitive decline persisted. While incident stroke was associated with a decrease in global cognition corresponding to approximately 7.9 years of cognitive aging it did not statistically differ by race (P=0.52).

The authors conduct a study which addresses an important issue of whether strokes disproportionately affect cognitive decline in the non-Hispanic black population. The racial disparities that exist in cognitive decline for the two populations would be difficult to discern as the contribution of multiple factors plays a role in the process. Contributions from genetics, socio-economic status and education levels, as well as multiple other factors play a significant role in cognitive decline in racial groups. One of the questions I have for the authors is whether they looked at varying types of cognitive declines (i.e. MCI vs vascular dementia vs Alzheimers) to see if incident stroke played a more significant role in the varying subtypes of dementia. They also acknowledge the limitation that strokes in certain areas were not analyzed as this may predispose an individual to develop more severe deficits in cognition than strokes in other regions. As imaging modalities improve and our understanding of dementia as well as the effect strokes in certain regions of the cerebrum have on functioning, we may be able to better discern the effect of vascular disease on cognitive decline.