Is there an association between ethnicity and incidence of dementia post-stroke? A cohort study using the UK Clinical Practice Research Datalink

Problem

The UK has over 1.2 million stroke survivors. Stroke is a major risk factor for dementia and is more common in ethnic minority groups. Some dementia risk factors such as hypertension and diabetes are also more common among ethnic minority groups and the proportion of elderly individuals from Black, Asian and other ethnic minorities (BAME) is set to increase in the future. We aimed to explore whether dementia incidence in adult stroke survivors differs by ethnicity, and to understand whether any differences are due to modifiable factors.

Approach

Using the UK Clinical Practice Research Datalink (CPRD) and linked Hospital Episode Statistics (HES) data, we conducted a cohort study among patients aged 40 years or more who had an incident stroke between 2005 and 2016. Patient follow-up started three months post-stroke until the earliest of either incident diagnosis of dementia, transfer out or practice, death, or end of study period. Ethnicity was defined using a previously used algorithm. Our study outcome was incident dementia based on clinical diagnoses recorded in CPRD or HES. We fitted multivariable Cox proportionate hazard models to estimate ethnic differences in the risk of post-stroke dementia, adjusting for major clinical and social confounders, taking the White ethnic group as the reference category and using age-at-stroke as the timescale.

Findings

Of 76,388 patients with an incident stroke, 15,996 were excluded as they developed dementia or transferred out within 3 months of stroke, or had pre-existing dementia at the time of the stroke.45,474 of the remaining 60,392 patients (75%) had ethnicity information so were included in our study (mean age at stroke 72.6 years, 49% female). 43,526 (95.7%) were from the White ethnic group, 885 (2%) South Asian, 543 (1.2%) Black, and 520 (1.1%) Mixed/Other. Median follow-up was 3.26 years and 4,624 (10.2%) developed post-stroke dementia. Compared to the White ethnic group, there was good evidence that those of South Asian ethnicity were 30% less likely to be diagnosed with dementia (adjusted Hazard Ratio (HR) 0.70, 95%CI 0.54-0.90), while there was no evidence of an association with being from Black ethnic group (adjusted HR 0.85, 95%CI 0.63-1.15) or of Mixed/Other ethnicity (adjusted HR 0.72, 95%CI 0.51-1.03).

Consequences

There was strong evidence that South Asians were at reduced risk of a dementia diagnosis post-stroke. There was also some indication the risk was reduced in Black and Mixed/Other ethnic groups, however the study was limited by small numbers. Mechanisms for this association remain unclear and we are currently exploring factors potentially influencing our results such as ethnic differences in premature exit from the study. Better understanding of this relationship could help in targeting interventions in communities most at risk of dementia post-stroke.