White Matter Microstructure Improves Stroke Risk Prediction in the General Population

Cluster-Based White Matter Signatures and the Risk of Dementia, Stroke, and Mortality in Community-Dwelling Adults

BACKGROUND AND OBJECTIVES

Markers of white matter (WM) injury on brain MRI are important indicators of brain health. Different patterns of WM atrophy, WM hyperintensities (WMHs), and microstructural integrity could reflect distinct pathologies and disease risks, but large-scale imaging studies investigating WM signatures are lacking. This study aims to identify distinct WM signatures using brain MRI in community-dwelling adults, determine underlying risk factor profiles, and assess risks of dementia, stroke, and mortality associated with each signature.

METHODS

Between 2005 and 2016, we measured WMH volume, WM volume, fractional anisotropy (FA), and mean diffusivity (MD) using automated pipelines on structural and diffusion MRI in community-dwelling adults aged older than 45 years of the Rotterdam study. Continuous surveillance was conducted for dementia, stroke, and mortality. We applied hierarchical clustering to identify separate WM injury clusters and Cox proportional hazard models to determine their risk of dementia, stroke, and mortality.

RESULTS

We included 5,279 participants (mean age 65.0 years, 56.0% women) and identified 4 distinct data-driven WM signatures: (1) above-average microstructural integrity and little WM atrophy and WMH; (2) above-average microstructural integrity and little WMH, but substantial WM atrophy; (3) poor microstructural integrity and substantial WMH, but little WM atrophy; and (4) poor microstructural integrity with substantial WMH and WM atrophy. Prevalence of cardiovascular risk factors, lacunes, and cerebral microbleeds was higher in clusters 3 and 4 than in clusters 1 and 2. During a median 10.7 years of follow-up, 291 participants developed dementia, 220 had a stroke, and 910 died. Compared with cluster 1, dementia risk was increased for all clusters, notably cluster 3 (hazard ratio [HR] 3.06, 95% CI 2.12-4.42), followed by cluster 4 (HR 2.31, 95% CI 1.58-3.37) and cluster 2 (HR 1.67, 95% CI 1.17-2.38). Compared with cluster 1, risk of stroke was higher only for clusters 3 (HR 1.55, 95% CI 1.02-2.37) and 4 (HR 1.94, 95% CI 1.30-2.89), whereas mortality risk was increased in all clusters (cluster 2: HR 1.27, 95% CI 1.06-1.53, cluster 3: HR 1.65, 95% CI 1.35-2.03, cluster 4: HR 1.76, 95% CI 1.44-2.15), compared with cluster 1. Models including clusters instead of an individual imaging marker showed a superior goodness of fit for dementia and mortality, but not for stroke.

DISCUSSION

Clustering can derive WM signatures that are differentially associated with dementia, stroke, and mortality risk. Future research should incorporate spatial information of imaging markers.

Effect of worry, depressed affect, and sensitivity to environmental stress owing to neurotic personality on MRI markers of cerebral small vessel disease: A univariable and multivariable Mendelian randomization study

OBJECTIVE

Neuroticism was found to be associated with cerebral small vessel disease (CSVD) in observational studies. We aimed to explore the causal relationship between distinct components of neuroticism and CSVD.

METHODS

Two-sample mendelian randomization (MR) study was conducted to explore the bidirectional causal relationships between three genetically distinct subclusters of neuroticism (depressed affect, worry, and sensitivity to environmental stress and adversity [SESA]) and MRI markers of CSVD using publicly available genome-wide association studies (GWAS) data. Inverse variance weighted (IVW) method was used for the primary causal estimates. Alternative MR approaches and extensive sensitivity analyses were conducted to ensure the robustness of the findings. Multivariable MR (MVMR) analysis was used to estimate the direct causal effects with adjustment of other known risk factors for CSVD.

RESULTS

Genetically determined SESA was significantly associated with reduced fractional anisotropy (FA) (beta: -1.94, 95%CI: -3.04 to -0.84, p=5.29e-4), and associated with increased mean diffusivity (MD) (beta=1.55, 95%CI: 0.29 to 2.81, p=0.016) and white matter hyperintensities (WMH) (beta=0.25, 95% CI: 0.03 to 0.47, p=0.029) at the nominally significant level. MVMR analysis suggested the significant associations remained significant after accounting for body mass index (BMI), smoking, alcohol drinking, type 2 diabetes (T2D), hypertension, and depression. The other two neuroticism subclusters (depressed affect and worry) didn't have significant causal effects on the MRI markers. In the reverse MR analysis with the MRI markers as exposures, no significant associations were found.

CONCLUSION

This study supported the casual role of SESA in the development of CSVD. Further research to explore the underlying mechanism are warranted.

Assessment of bidirectional relationships between brain imaging-derived phenotypes and stroke: a Mendelian randomization study

BACKGROUND

Stroke is a major cause of mortality and long-term disability worldwide. Whether the associations between brain imaging-derived phenotypes (IDPs) and stroke are causal is uncertain.

METHODS

We performed two-sample bidirectional Mendelian randomization (MR) analyses to explore the causal associations between IDPs and stroke. Summary data of 587 brain IDPs (up to 33,224 individuals) from the UK Biobank and five stroke types (sample size range from 301,663 to 446,696, case number range from 5,386 to 40,585) from the MEGASTROKE consortium were used.

RESULTS

Forward MR indicated 14 IDPs belong to projection fibers or association fibers were associated with stroke. For example, higher genetically determined mean diffusivity (MD) in the right external capsule was causally associated with an increased risk of small vessel stroke (IVW OR = 2.76, 95% CI 2.07 to 3.68, P = 5.87 × 10^-12). Reverse MR indicated that genetically determined higher risk of any ischemic stroke was associated with increased isotropic or free water volume fraction (ISOVF) in body of corpus callosum (IVW β = 0.23, 95% CI 0.14 to 0.33, P = 3.22 × 10^-7). This IDP is a commissural fiber and it is not included in the IDPs identified by forward MR.

CONCLUSIONS

We identified 14 IDPs with statistically significant evidence of causal effects on stroke or stroke subtypes. We also identified potential causal effects of stroke on one IDP of commissural fiber. These findings might guide further work toward identifying preventative strategies at the brain imaging levels.

Assessment of incidence of cerebral vascular diseases and prediction of stroke risk in chronic obstructive pulmonary disease patients using multimodal biomarkers

BACKGROUND

Early assessment of cerebrovascular disease in chronic obstructive pulmonary disease (COPD) patients is an important issue for a favorable influence on the quality of life.

METHODOLOGY

This cross-sectional case-control study was conducted on 38 eligible COPD patients (mean age 55.5 ± 11.5, 25 males, and 13 females) and 26 age-/sex-matched healthy controls. All participants were subjected to stroke risk screening instruments that included the Stroke Riskometer™, the Framingham 10-Year Risk Score, the stroke risk screening tool (the Department of Disease Control of Thailand), the My Risk Stroke Calculator, and Q Stroke. Radiologically, diffusion tensor imaging (DTI) and echo-gradient MRI (T2 star) T2 star imaging were done. Color-coded duplex sonography was done. Laboratory investigations included C-reactive protein (CRP), serum amyloid A, plasma fibrinogen level, serum IL6, 8-Isoprostane, vWF and urinary albumin creatinine ratio.

RESULTS

Stroke risk screening instruments revealed a significant increase in COPD patients. DTI showed a significant bilateral reduction in fractional isotropy and a significant bilateral increase in mean diffusivity of white matter through many areas in COPD patients. Patients also had a significant increase of intima-media thickness, presence of atherosclerotic focal thicknesses or plaques on duplex sonography. There was a significant elevation of CRP, serum amyloid A, plasma fibrinogen level, serum IL6, 8-isoprostane, von Willebrand factor (vWF), and urinary albumin creatinine ratio in COPD patients.

CONCLUSION

COPD patients had an increased risk for stroke that could be assessed on stroke risk screening instruments, DTI, T2 star, duplex sonography, and laboratory investigation and could be correlated with the severity of the disease.

Risk Stratification Tool for Ischemic Stroke: A Risk Assessment Model Based on Traditional Risk Factors Combined With White Matter Lesions and Retinal Vascular Caliber

Objective: This study aims to establish a risk assessment model based on traditional risk factors combined with the Fazekas classification of white matter lesions and retinal vascular caliber for screening the patients at high risk of ischemic stroke.

Methods: This study included 296 patients (128 cases of ischemic stroke and 168 cases in the normal control group). The basic data of the patients were collected. Color fundus photography was performed after pupil dilation, and the retinal vascular caliber was measured using semiautomated vascular measurement software (IVAN Software, Sydney, Australia). The severity of white matter lesions (WML) on cranial nuclear magnetic fluid-attenuated inversion recovery images were assessed using the Fazekas scale. Moreover, logistic regression analysis was used to establish different risk assessment models for ischemic stroke. The effects of models were evaluated through the receiver operating characteristic (ROC) curve and the Delong test compared area under the curve.

Results: The sensitivity and specificity of models 1 (the traditional risk factor model), 2 (the retinal vascular caliber model), 3 (the WML model), and 4 (the combined the traditional risk factor, WML and central retinal artery equivalent (CRAE) model) were 71 and 55%, 48 and 71%, 49 and 67%, and 68 and 68.5% with areas under the curve of 0.658, 0.586, 0.601, and 0.708, respectively. The area under the receiver operating characteristic curve in models 1, 2, 3, and 4 showed statistically significant differences. Moreover, no statistical significance exists in the pairwise comparison of other models.

Conclusion: The risk assessment model of ischemic stroke combined with Fazekas grade of WML and CRAE is superior to the traditional risk factor and the single-index model. This model is helpful for risk stratification of high-risk stroke patients.

Emerging role of white matter lesions in cerebrovascular disease

White matter lesions have been implicated in the setting of stroke, dementia, intracerebral haemorrhage, several other cerebrovascular conditions, migraine, various neuroimmunological diseases like multiple sclerosis, disorders of metabolism, mitochondrial diseases and others. While much is understood vis a vis neuroimmunological conditions, our knowledge of the pathophysiology of these lesions, and their role in, and implications to, management of cerebrovascular diseases or stroke, especially in the elderly, are limited. Several clinical assessment tools are available for delineating white matter lesions in clinical practice. However, their incorporation into clinical decision-making and specifically prognosis and management of patients is suboptimal for use in standards of care. This article sought to provide an overview of the current knowledge and recent advances on pathophysiology, as well as clinical and radiological assessment, of white matter lesions with a focus on its development, progression and clinical implications in cerebrovascular diseases. Key indications for clinical practice and recommendations on future areas of research are also discussed. Finally, a conceptual proposal on putative mechanisms underlying pathogenesis of white matter lesions in cerebrovascular disease has been presented. Understanding of pathophysiology of white matter lesions and how they mediate outcomes is important to develop therapeutic strategies.

Coronary Artery Calcium Assessed Years Before Was Positively Associated With Subtle White Matter Injury of the Brain in Asymptomatic Middle-Aged Men: The Framingham Heart Study

BACKGROUND

Using magnetic resonance diffusion tensor imaging, we previously showed a cross-sectional association between carotid-femoral pulse wave velocity, a measure of aortic stiffness, and subtle white matter injury in clinically asymptomatic middle-age adults. While coronary artery calcium (CAC) is a robust measure of atherosclerosis, and a predictor of stroke and dementia, whether it predicts diffusion tensor imaging-based subtle white matter injury in the brain remains unknown.

METHODS

In FHS (Framingham Heart Study), an observational study, third-generation participants were assessed for CAC (2002-2005) and brain magnetic resonance imaging (2009-2014). Outcomes were diffusion tensor imaging-based measures; free water, fractional anisotropy, and peak width of mean diffusivity. After excluding the participants with neurological conditions and missing covariates, we categorized participants into 3 groups according to CAC score (0, 0 < to 100, and >100) and calculated a linear trend across the CAC groups. In secondary analyses treating CAC score as continuous, we computed slope of the outcomes per 20 to 80th percentiles higher log-transformed CAC score using linear regression.

RESULTS

In a total of 1052 individuals analyzed (mean age 45.4 years, 45.4% women), 71.6%, 22.4%, and 6.0% had CAC score of 0, 0 < to 100, and >100, respectively. We observed a significant linear trend of fractional anisotropy, but not other measures, across the CAC groups after multivariable adjustment. In the secondary analyses, CAC was associated with lower fractional anisotropy in men but not in women.

CONCLUSIONS

CAC may be a promising tool to predict prevalent subtle white matter injury of the brain in asymptomatic middle-aged men.

A systematic review of the status and methodological considerations for estimating risk of first ever stroke in the general population

AIMS

The methodological quality of development, validation, and modification of those models have not been evaluated via a thoroughly literature review. This study aims to describe the overall status and evaluate the methodological quality of risk prediction models for stroke incidence in the general population.

METHODS

We searched the database of EMBASE and MEDLINE by the combination of subject words and key words to collect the research on stroke risk prediction model in the general population. The retrieval time was from the establishment of the database to September 2019. It should be mentioned that risk of bias for each model was assessed, and data on population characteristics and model performance was also extracted.

RESULTS

The search screened 11,386 peer-reviewed publications and 57 citation searching, of which 48 were included in the review, describing the development of 51 prediction models, 47 external validation models, and 12 modification models. Among 51 development models, the predicted outcome concentrated on fatal or non-fatal stroke (n = 37, 73%). Thirty-nine development models (76%) were without internal validation. C-statistic or AUC was adopted for discrimination in 80% models, and Hosmer-Lemeshow test (n = 25, 49%) was also performed for calibration. Twenty-six development models (53%) were externally validated, among which only 2 (8%) were validated by independent researchers. Risk prediction performance was improved when models were modified by adding novel risk factors, such as the internal carotid artery plaque and intima-media thickness.

CONCLUSION

Models for predicting stroke occurrence need further external validation, recalibration, or modification in different populations, to help interpret those models in the practice of stroke prevention.

Combined lifestyle factors are associated with the risk of ischaemic stroke in a Chinese population

PURPOSE

Lifestyle plays an important role in the development of ischaemic stroke (IS). The objective of this study was to evaluate the association between combined lifestyle factors and the risk of IS in an eastern Chinese population.

METHODS

We collected lifestyle information from 191 patients with IS admitted to the second affiliated hospital of Soochow University and 575 control subjects from community clinics using a structured questionnaire. After division into training and test datasets, regularised stepwise logistic regression, least absolute shrinkage and selection operator regression and genetic algorithm models were used to identify lifestyle factors associated with IS. The improved discriminative ability by adding the lifestyle factors was determined by c-index and reclassification analysis. The final model was validated in the test dataset.

RESULTS

After controlling for conventional cardiovascular disease (CVD) risk factors, preferences for fruits (OR (95% CI): 0.29 (0.18-0.46), p<0.001) and soy products (0.47 (0.29-0.75), p=0.002) were negatively associated with IS, while lower life satisfaction (mildly satisfied: 2.15 (1.27-3.63), p=0.004; not satisfied: 6.39 (1.76-25.44), p=0.006) was positively associated with IS. Adding these factors to a basic CVD risk model improved the c-index (0.825 vs 0.753, p<0.001) and reclassification for IS (net reclassification index (95% CI): 18.49% (7.90%-29.08%), integrated discrimination index (95% CI): 0.11% (0.08%-0.14%), p<0.001). The model with lifestyle factors achieved a c-index of 0.813 and good calibration in the test dataset.

CONCLUSIONS

Our results showed that combined lifestyle factors including dietary pattern and life satisfaction are independently associated with the risk of IS.

The etiology, manifestations, and therapy of chronic cerebrovascular diseases

The paper presents the current etiopathogenetic classification of chronic cerebrovascular diseases (CVD) and discusses the role of hypertension, cerebral amyloid angiopathy, and genetically determined syndromes in the development of this pathological condition. It gives recommendations for the neuroradiological diagnosis of chronic CVD in accordance with the international standards. The paper discusses the clinical manifestations of chronic CVD, primarily vascular cognitive impairment. It discusses international guidelines for the examination and treatment of patients with chronic CVD, as well as the rules for stroke prevention in this patient cohort. The possibilities of pathogenetically based therapy in decreasing the severity of vascular cognitive impairment in the presence of chronic CVD are also highlighted.

Objectives, design and main findings until 2020 from the Rotterdam Study

The Rotterdam Study is an ongoing prospective cohort study that started in 1990 in the city of Rotterdam, The Netherlands. The study aims to unravel etiology, preclinical course, natural history and potential targets for intervention for chronic diseases in mid-life and late-life. The study focuses on cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, otolaryngological, locomotor, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. Since 2016, the cohort is being expanded by persons aged 40 years and over. The findings of the Rotterdam Study have been presented in over 1700 research articles and reports. This article provides an update on the rationale and design of the study. It also presents a summary of the major findings from the preceding 3 years and outlines developments for the coming period.

Neuroimaging of Cerebral Small Vessel Disease and Age-Related Cognitive Changes

Subclinical cerebrovascular disease is frequently identified in neuroimaging studies and is thought to play a role in the pathogenesis of cognitive disorders. Identifying the etiologies of different types of lesions may help investigators differentiate between age-related and pathological cerebrovascular damage in cognitive aging. In this review article, we aim to describe the epidemiology and etiology of various brain magnetic resonance imaging (MRI) measures of vascular damage in cognitively normal, older adult populations. We focus here on population-based prospective cohort studies of cognitively unimpaired older adults, as well as discuss the heterogeneity of MRI findings and their relationships with cognition. This review article emphasizes the need for a better understanding of subclinical cerebrovascular disease in cognitively normal populations, in order to more effectively identify and prevent cognitive decline in our rapidly aging population.

Innovative MRI Techniques in Neuroimaging Approaches for Cerebrovascular Diseases and Vascular Cognitive Impairment

Cognitive impairment and dementia are recognized as major threats to public health. Many studies have shown the important role played by challenges to the cerebral vasculature and the neurovascular unit. To investigate the structural and functional characteristics of the brain, MRI has proven an invaluable tool for visualizing the internal organs of patients and analyzing the parameters related to neuronal activation and blood flow in vivo. Different strategies of imaging can be combined to obtain various parameters: (i) measures of cortical and subcortical structures (cortical thickness, subcortical structures volume); (ii) evaluation of microstructural characteristics of the white matter (fractional anisotropy, mean diffusivity); (iii) neuronal activation and synchronicity to identify functional networks across different regions (functional connectivity between specific regions, graph measures of specific nodes); and (iv) structure of the cerebral vasculature and its efficacy in irrorating the brain (main vessel diameter, cerebral perfusion). The high amount of data obtainable from multi-modal sources calls for methods of advanced analysis, like machine-learning algorithms that allow the discrimination of the most informative features, to comprehensively characterize the cerebrovascular network into specific and sensitive biomarkers. By using the same techniques of human imaging in pre-clinical research, we can also investigate the mechanisms underlying the pathophysiological alterations identified in patients by imaging, with the chance of looking for molecular mechanisms to recover the pathology or hamper its progression.

Cognitive functions and white matter lesions on magnetic resonance images in a sample of normal Iranian population with cardiovascular risk factors

PURPOSE

Due to a suggestive three-way relationship between brain structural disorders, microvascular lesions, and cognitive impairments, we aimed to examine the association of the volume and number of white matter hyperintensity lesions and lacunar infarcts with cognitive impairment among patients with cardiovascular risk factors in a sample of the Iranian population.

MATERIALS AND METHODS

This study was conducted on a total number of 156 normal subjects aged 30-74 years with cardiovascular risk factors. We used the Framingham general cardiovascular risk factors prediction model to calculate the likelihood of each risk factor. The total number of lacunar infarcts and the volume of white matter hyperintensity lesion were calculated in brain magnetic resonance imaging. Cognition status was assessed using the Montreal Cognitive Assessment questionnaire.

RESULTS

An adverse association was revealed between Montreal Cognitive Assessment score and different cardiovascular risk profiles including the Framingham body mass index score ( p < 0.001) and the Framingham lipid score ( p < 0.001). The total volume of white matter hyperintensity was negatively associated with total Montreal Cognitive Assessment cognition score ( p < 0.001). Our study also showed an adverse association between total number of lacunar infarcts and total Montreal Cognitive Assessment cognition score ( p = 0.038) and with some cognition components including memory ( p = 0.013), attention ( p = 0.037), abstraction ( p = 0.046), and orientation ( p = 0.002).

CONCLUSION

Periventricular lesions are associated with impaired memory, language, and visuoconstruction while subcortical lesions are associated with impairment in naming, attention, language, and abstraction functions in normal subjects with cardiovascular risk factors but without cardiovascular or cerebrovascular disorders.

Non-obese fatty liver disease is associated with lacunar infarct

BACKGROUND/AIMS

Lacunar infarct, a small subcortical ischaemic lesion, is a known risk factor for future cognitive impairment, dementia and stroke. We evaluated the relationship between fatty liver disease (FLD) and lacunar infarct in a healthy general population.

METHODS

Subjects who underwent brain magnetic resonance imaging (MRI) and abdominal ultrasonography (US) during health check-ups from 2007 to 2009 were included. FLD was diagnosed by US. Subjects with a history of cerebrovascular disease, radiological findings consistent with cerebrovascular stenosis or cerebral small vessel disease were excluded.

RESULTS

Of the 1277 subjects, 54 (4.2%) exhibited lacunar infarct, and 514 (40.3%) had FLD. Subjects with lacunar infarct had a higher prevalence of FLD (59.3% vs 39.4%, P = .004). There was significant interaction between obesity (BMI < 25 kg/m² vs ≥ 25 kg/m² ) and FLD for lacunar infarct (P for interaction = .024). Subgroup analysis revealed that non-obese FLD was more common in the subjects with lacunar infarct than those without (51.7% vs 23.5%, P = .001). However, there was no significant difference in the obese FLD prevalence between these 2 groups. In multivariate models adjusted by age, sex, smoking, alcohol, hypertension and diabetes, FLD was significantly associated with lacunar infarct (odds ratio [OR] 1.97; 95% confidence interval [CI] 1.08-3.58; P = .027). Non-obese FLD was associated with lacunar infarct (OR 3.58; 95% CI 1.63-7.89; P = .002); however, this association remained insignificant in obese FLD. Instead, ageing and hypertension were independent risk factors for lacunar infarct in the obese population.

CONCLUSIONS

FLD is significantly associated with lacunar infarct, independent of traditional risk factors. This association was prominent in the non-obese population.

The Rotterdam Study: 2018 update on objectives, design and main results

The Rotterdam Study is a prospective cohort study ongoing since 1990 in the city of Rotterdam in The Netherlands. The study targets cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, otolaryngological, locomotor, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. Since 2016, the cohort is being expanded by persons aged 40 years and over. The findings of the Rotterdam Study have been presented in over 1500 research articles and reports (see www.erasmus-epidemiology.nl/rotterdamstudy ). This article gives the rationale of the study and its design. It also presents a summary of the major findings and an update of the objectives and methods.

Changes to white matter microstructure in transient ischemic attack: A longitudinal diffusion tensor imaging study

Transient ischemic attack (TIA) is associated with localized ischemic changes, identifiable by diffusion-weighted imaging. Past research has not considered whether TIA is also associated with diffuse changes to white matter microstructure; further past work has not tracked changes longitudinally. Here we examine whole-brain changes in fractional anisotropy (FA) in individuals with TIA presenting with sensorimotor symptoms. Twenty individuals with a recent (within 30 days) TIA and 12 healthy older adults were recruited. Participants underwent 3.0 T diffusion MRI at baseline; scans were repeated for the TIA group 90 days post-TIA. Track-based spatial statistics (TBSS) was used to conduct a voxel-wise analysis of FA between groups. FA was significantly lower in the TIA group relative to healthy controls, primarily in anterior white matter tracts including: forceps minor, anterior thalamic radiations, cingulum, inferior fronto-occipital fasciculus, and corticospinal tract. TBSS results informed an ROI-based longitudinal examination of FA in the TIA group. There were no changes to TBSS-identified clusters, forceps minor, or the corticospinal tract over time. There was lower FA in the anterior thalamic radiations in the TIA-affected hemisphere at baseline, but no difference between hemispheres at 90 days. In summary, individuals with TIA presenting with sensorimotor symptoms have decreased FA in tracts that are also implicated in sensorimotor function, which outlast the clinical symptoms associated with TIA. This suggests a more profound type of brain damage associated with TIA than has been typically described in past work. Diffusion tensor imaging may have utility as a marker of TIA-associated changes to white matter pathways. Hum Brain Mapp 38:5795-5803, 2017. © 2017 Wiley Periodicals, Inc.

Endothelial Function Is Associated with White Matter Microstructure and Executive Function in Older Adults

Age-related declines in endothelial function can lead to cognitive decline. However, little is known about the relationships between endothelial function and specific neurocognitive functions. This study explored the relationship between measures of endothelial function (reactive hyperemia index; RHI), white matter (WM) health (fractional anisotropy, FA, and WM hyperintensity volume, WMH), and executive function (Trail Making Test (TMT); Trail B - Trail A). Participants were 36 older adults between the ages of 59 and 69 (mean age = 63.89 years, SD = 2.94). WMH volume showed no relationship with RHI or executive function. However, there was a positive relationship between RHI and FA in the genu and body of the corpus callosum. In addition, higher RHI and FA were each associated with better executive task performance. Tractography was used to localize the WM tracts associated with RHI to specific portions of cortex. Results indicated that the RHI-FA relationship observed in the corpus callosum primarily involved tracts interconnecting frontal regions, including the superior frontal gyrus (SFG) and frontopolar cortex, linked with executive function. These findings suggest that superior endothelial function may help to attenuate age-related declines in WM microstructure in portions of the corpus callosum that interconnect prefrontal brain regions involved in executive function.

Advanced Neuroimaging of Cerebral Small Vessel Disease

Cerebral small vessel disease (SVD) is characterised by damage to deep grey and white matter structures of the brain and is responsible for a diverse range of clinical problems that include stroke and dementia. In this review, we describe advances in neuroimaging published since January 2015, mainly with magnetic resonance imaging (MRI), that, in general, are improving quantification, observation and investigation of SVD focussing on three areas: quantifying the total SVD burden, imaging brain microstructural integrity and imaging vascular malfunction. Methods to capture ‘whole brain SVD burden’ across the spectrum of SVD imaging changes will be useful for patient stratification in clinical trials, an approach that we are already testing. More sophisticated imaging measures of SVD microstructural damage are allowing the disease to be studied at earlier stages, will help identify specific factors that are important in development of overt SVD imaging features and in understanding why specific clinical consequences may occur. Imaging vascular function will help establish the precise blood vessel and blood flow alterations at early disease stages and, together with microstructural integrity measures, may provide important surrogate endpoints in clinical trials testing new interventions. Better knowledge of SVD pathophysiology will help identify new treatment targets, improve patient stratification and may in future increase efficiency of clinical trials through smaller sample sizes or shorter follow-up periods. However, most of these methods are not yet sufficiently mature to use with confidence in clinical trials, although rapid advances in the field suggest that reliable quantification of SVD lesion burden, tissue microstructural integrity and vascular dysfunction are imminent.

Integrity of normal-appearing white matter and functional outcomes after acute ischemic stroke

OBJECTIVE

To characterize the effect of white matter microstructural integrity on cerebral tissue and long-term functional outcomes after acute ischemic stroke (AIS).

METHODS

Consecutive AIS patients with brain MRI acquired within 48 hours of symptom onset and 90-day modified Rankin Scale (mRS) score were included. Acute infarct volume on diffusion-weighted imaging (DWIv) and white matter hyperintensity volume (WMHv) on T2 fluid-attenuated inversion recovery MRI were measured. Median fractional anisotropy (FA), mean diffusivity, radial diffusivity, and axial diffusivity values were calculated within normal-appearing white matter (NAWM) in the hemisphere contralateral to the acute lesion. Regression models were used to assess the association between diffusivity metrics and acute cerebral tissue and long-term functional outcomes in AIS. Level of significance was set at p < 0.05 for all analyses.

RESULTS

Among 305 AIS patients with DWIv and mRS score, mean age was 64.4 ± 15.9 years, and 183 participants (60%) were male. Median NIH Stroke Scale (NIHSS) score was 3 (interquartile range [IQR] 1-8), and median normalized WMHv was 6.19 cm³ (IQR 3.0-12.6 cm³). Admission stroke severity (β = 0.16, p < 0.0001) and small vessel stroke subtype (β = -1.53, p < 0.0001), but not diffusivity metrics, were independently associated with DWIv. However, median FA in contralesional NAWM was independently associated with mRS score (β = -9.74, p = 0.02), along with age, female sex, NIHSS score, and DWIv.

CONCLUSIONS

FA decrease in NAWM contralateral to the acute infarct is associated with worse mRS category at 90 days after stroke. These data suggest that white matter integrity may contribute to functional recovery after stroke.