We found a high frequency of post-stroke cognitive impairment assessed a minimum of 3-months after stroke in a consecutive series of patients evaluated at the primary referral hospital in Uganda. The overall frequency of 66.4% is higher than a previous 43% estimate in this population (29). The previous study, conducted in 2005, involved a smaller sample of participants (n = 77). Our result is consistent with findings in Nigeria (67.4%), Ghana (72.8%), Korea (62.6%), and Norway (52.1%) (3, 30, 31). A meta-analysis of 65 observational studies, published in 2019, reported sparse data on cognitive impairment in sub-Saharan Africa, but found overall prevalence among African people aged 5- years or older at 30–40% (32). The high prevalence may be because most stroke patients in this population present late to health facilities and to the lack of cognitive rehabilitation intervention availability in Uganda’s existing post stroke management care protocols.
In multivariable analyses, we adjusted for variables associated with cognitive outcomes in univariable analyses and for potential confounders identified in other studies (i.e., age, sex, and stroke severity) (22). Our univariate analysis found that age > 60-years was associated with post stroke cognitive impairment, consistent with prior studies in other populations (20). In contrast to some other studies (33, 34), we found no associations between sex and stroke severity (as measured by NIHSS scores) with MCI. The lack of associations may be related to the timing of our assessments, the type of cognitive assessments, and differences in educational attainment between study populations. The extent of formal education is protective against cognitive impairment in vascular dementia, Alzheimer’s disease and mild cognitive impairment (3, 35). A higher educational level increases the brain’s cognition reserve, which may lead to improved compensation with aging and brain injury (20).
We found higher LDL-C was associated with greater cognitive impairment. This result is consistent with a previous cross-sectional analysis from four U.S. cities which found a positive association between LDL-C levels and cognitive measures (10, 36). Additionally, findings from the Northern Manhattan Stroke Study showed that higher LDL-C was associated with the risk of incident vascular dementia (10, 37). The mechanisms underlying the association between LDL-C and cognitive impairment are unknown, and different explanations have been proposed (8, 38, 39). A recent study showed that LDL -C activates the secretion of pro- inflammatory mediators such as tumor necrosis factor alpha and interleukin-6 and decreased the BBB membrane injury, a contributory factor to the development and progression of cognitive impairment (40, 41).
High mRS score (i.e., 3 − 5) was independently associated with cognitive impairment. Scores 3–5 are associated with high to total patient handicap and reliance on others in performing activities of daily living (42). The impact of a stroke goes far beyond physical disability (43), impairing higher-order cognitive functions such as motor control, organization, problem solving, and memory. Stroke survivors who are physically dependent and more impaired tend to perform poorly in these tasks (43).
Patient functional dependence as assessed by the BI predicted cognitive impairment as a single variable; however, the association between BI and cognitive impairment attenuated as was not significant when controlling for potential confounding variables in the multivariate analysis. This could be due to collinearity between the independent variables or it could also be a result of the BI instrument. It has been postulated that functional dependence is not a pure personal characteristic but is instead a gap between one’s ability and one’s personal needs suggesting the existence of other environmental, social, and individual adaptations in contributing to activities of daily living (44). In addition, the sensitivity of the BI to distinguish between high and low performers is limited (45). It is not efficient in detecting problems in more complex social skills as it only involves 8 basic daily life tasks. Only severe cognitive impairment may interfere with these tasks (45).
Our study has several limitations. Our relatively small sample size could reduce our statistical power to identify associations of lower effect size. Because of the cross-sectional design, we cannot provide evidence of causal relationships between putative predictors and post-stroke cognitive impairment. Dementia involves a change in function and cognition, but we did not conduct longitudinal assessments and in some cases, relied on proxy reports for some variables (3). There is also a potential inception cohort bias because our sample included only participants seen at a single national referral hospital. The MoCA is not validated in a sub-Saharan African population and therefore does not take account of certain linguistic and cultural variables which may affect interpretation of the MoCA across different countries. In addition, participant level of education affects the results of some screening tests, including the MoCA, resulting in a possible overestimation of cognitive impairment among those who are illiterate. Using a MoCA cut-off of 19 to classify cognitive impairment in this population rather than the more common 26 points, however, mitigates this effect. (4) Most of the study participants had a relatively mild stroke and our results may not be generalizable to those with a more severe or very mild stroke, or to those who have specific deficits (e.g., aphasia) that precluded cognitive assessment.
Limitations notwithstanding, this study provides unique data on the frequency and risk factors for post-stroke cognitive impairments in Uganda, a resource constrained country in sub-Saharan Africa. The data are helpful for creating public awareness, influencing policy recommendations, and guiding further research that may lead to effective interventions.