Slowed Information Processing Speed at Four Years Poststroke: Evidence and Predictors from a Population-Based Follow-up Study

https://doi.org/10.1016/j.jstrokecerebrovasdis.2019.104513Get rights and content

Abstract

Background and Purpose

Slowed Information Processing Speed (IPS) is a commonly reported cognitive deficit following stroke, affecting up to 50% to 70 % of stroke survivors. IPS has a major influence on poststroke cognitive dysfunction, affecting quality of life and increasing dependence on others. Few studies have examined predictors of slow IPS after stroke, and there is a paucity of data in terms of long-term prevalence. This study examined baseline predictors associated with long-term slow IPS in a population-based stroke incidence cohort, 4 years after stroke onset.

Methods

Adults with stroke (n = 133, m = 71.1 ± 13.5 years) completed the Symbol Digit Modalities Test (SDMT) at 4 years poststroke. Baseline predictors were obtained within 2 weeks of the acute event. Multivariate regression linear and logistic models were used to identify baseline predictors (reported as OR with 95%CI) and prevalence of impaired IPS at 4-years.

Results

51% of people with stroke had low scores on the SDMT as indicated by a score of −1.0 SD to −2.5 SD (ranging from low to very low respectively). There were significant associations between slow IPS at 4-years after controlling for age and education level and the following baseline factors: older age (>75 years) (OR 3.03, 95% CI .9-9.3,P = .05), previous stroke (OR 2.74, 95% CI 1.0-7.4,P = .05), high cholesterol (OR 2.72, 95% CI 1.3-5.4,p = .01), hypertension (OR 1.82, 95% CI 0.9-3.6,p = .05), and presence of coronary artery disease (OR 3.35, 95% CI 1.6-9.6,P = .01), or arrhythmia (OR 4.40, 95% CI 1.5-12.4,P = .01).

Conclusions

Even after 4-years poststroke, slowed IPS is highly prevalent, with comorbid vascular risk factors significantly contributing to persistent impaired IPS. Early identification of adults who are at higher risk of deficits in IPS is vital to targeting the timely delivery of cognitive rehabilitation interventions, improving overall outcomes.

Introduction

Cognitive impairment is a commonly reported sequalae after stroke, with estimated rates of 35%-70% in the postacute and chronic phases.1 There is no consensus as to the true profile of domain–specific cognitive deficits in this population. The profile varies depending on myriad of factors including lesion side,2 vascular territory3 stroke subtypes4 and anatomic localisation.5 Despite these variabilities, considerable evidence indicates that deficits in Information Processing Speed (IPS) commonly occur in this population. That is, slowed IPS ranks high on the list of self-report cognitive complaints by stroke patients.6 Objectively, at the acute phase of stroke, up to 70% of adults with stroke may experience slow IPS, with symptoms quite robust to rehabilitation.7 These impairments have also been frequently identified as the most severe cognitive deficit subsequent to stroke.8 IPS is thought to reflect the efficiency of cognitive function. It refers to the ability to complete a cognitive task or process information within a defined period of time. IPS has long been considered an essential component of intellectual abilities.9 That is, fast and efficient information processing is advantageous as it makes limited cognitive resources more available for higher order cognitive tasks.10 It has been postulated that IPS is an intrinsic part of many cognitive functions, and that slowed IPS may cause deficits in for example memory, attention, and executive functioning. There is also evidence that deficits found in these cognitive domains are attenuated when the influence of IPS is taken into account.11 It is therefore not surprising that deficits in IPS seriously interferes with everyday functioning. It impacts performance on everyday tasks12 and can adversely affect quality of life, community reintegration, and functional recovery in stroke patients.13,14

The underlying biological mechanisms which contribute to slow IPS following stroke occur when the brain is deprived of oxygen and nutrients causing axons to degrade, promoting the demyelination process which decreases transmission of messages along neural pathways.15 While not considered a stand-alone domain, IPS is a key cognitive resource which influences higher-order domains such as attention and executive functioning, and is an essential element to intellectual ability.16

Given its importance in predicting recovery, and their interference with quality of life, identification of those patients who are at risk of experiencing slow IPS is crucial in order to guide cognitive rehabilitation soon after stroke. In the acute stages of recovery, several factors have been identified that contribute to slow IPS. This includes location of stroke (right hemisphere), size of infarct, white matter deterioration, and age.17 Vascular risk factors such as elevated blood pressure, body mass index, blood glucose levels and physical activity have also been independently associated with slower IPS.18 Studies examining ischemic stroke subtypes (as defined by OCSP classification) and their association with cognitive function, have found those patients who experience total anterior infarcts (TACI) performed significantly worse on IPS compared to other ischemic stroke sub-types.4 Finally, several studies have found that people with impaired IPS are more likely to suffer from subcortical strokes, including the basal ganglia and thalamus areas.19

Over the past few years the symbol digit modalities test (SDMT) has become one of the most commonly used neuropsychological tests of IPS.20 Although no neuropsychological measure can be claimed to be process pure, research to date strongly suggests that cognitive speed is the prime determinant of the coding task performance, with other elementary mental processes such as working memory and selective attention playing a subsidiary role.21 As such, the SDMT is a valid and reliable measure of IPS as it can determine differences in performance which reflect the variation in the time taken to execute the relevant cognitive operations needed by the task.

To date, there has been a lack of research exploring the predictors of slow IPS in the chronic stages of stroke recovery. If in fact, longitudinal data exploring the incidence of slow IPS following stroke is scarce. Therefore, the aim of this study was to identify the long-term prevalence and predictors of slow IPS in a cohort of four-year stroke survivors.

Section snippets

Materials and Methods

This study received ethical approval from the Health and Disability Ethics Committee (reference NTX/10/90/090/AM07) and the Auckland University of Technology Ethics Committee (reference AUTEC 11/297).

Demographic, Stroke Related Characteristics and Vascular Risk Factors for the Sample

Table 1 summarises the characteristics of the sample (n = 133), providing descriptive information on the demographic, stroke related characteristics and vascular risk factors. In brief, the average time since stroke was 3.9 years ± 5.6 (ranging from 3.5 to 4.5 years). Mean age of the sample was 71.1 ± 13.5 years (ranging from 28 to 96 years). At the time of stroke, Europeans were older by an average of 15 years compared to Non-European. The majority of the sample were NZ European, (n = 106,

Discussion

This study examined the prevalence, and predictors associated with slowed IPS 4 years after stroke. IPS was affected in the majority of this cohort (51%). While there is considerable evidence that IPS is severely affected in the acute stage following stroke, there is limited data on long-term prevalence.

In terms of sociodemographic factors increased age, and unemployment status at baseline were significantly associated with slow IPS. Those stroke survivors who were not working were more likely

Summary

Our population-based study is one of the few which has provided strong evidence that slowed information processing speed following stroke is present in the long-term after stroke. Sociodemographic and vascular risk factors play an important role in the prevalence of impaired IPS following stroke. While some of these factors can be modified (through primary prevention strategies), others are more complex and require further research. Although the relationship between slowed IPS and stroke

Acknowledgments

ARCOS IV was funded by the Health Research Council of New Zealand and Neurological Foundation of New Zealand. We acknowledge the ARCOS IV Steering Committee, the ARCOS IV research assistants and research participants.

Conflict of Interest

None.

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      Cognitive impairment affects approximately 40 % of individuals who survive a stroke (Sexton, 2019). Specifically, processing speed and executive functions are often impaired after stroke (Knopman, 2009; Pohjasvaara, 2002), and are associated with poorer functional outcomes Barker-Collo et al., 2010, increased dependency Narasimhalu et al., 2011, and reduced employment (Mahon, 2020) in individuals with chronic stroke. Despite its high prevalence and clinical importance, we do not understand the patterns of brain damage associated with post-stroke cognitive impairment.

    Funding: This research was funded by the Health Research Council of New Zealand (HRC 10/458) and the Neurological Foundation of New Zealand (1423-GS).

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