Relationships between white matter hyperintensities, cerebral amyloid angiopathy and dementia in a population-based sample of the oldest old

Magnetic resonance imaging of white matter in Alzheimer's disease: a global bibliometric analysis from 1990 to 2022

Background

Alzheimer's disease (AD) is a common, progressive, irreversible, and fatal neurodegenerative disorder with rapidly increasing worldwide incidence. Although much research on magnetic resonance imaging (MRI) of the white matter (WM) in AD has been published, no bibliometric analysis study has investigated this issue. Thus, this study aimed to provide an overview of the current status, hotspots, and trends in MRI of WM in AD.

Methods

We searched for records related to MRI studies of WM in AD from 1990 to 2022 in the Web of Science Core Collection (WOSCC) database. CiteSpace (version 5.1.R8) and VOSviewer (version 1.6.19) software were used for bibliometric analyses.

Results

A total of 2,199 articles were obtained from this study. From 1990 to 2022, the number of published articles showed exponential growth of y = 4.1374e^0.1294x, with an average of 17.9 articles per year. The top country and institutions were the United States and the University of California Davis, accounting for 44.52 and 5.32% of the total studies, respectively. The most productive journal was Neurology, and the most co-cited journal was Lancet Neurology. Decarli C was the most productive author. The current research frontier trend focuses on the association between small vessel disease and AD, the clinical application and exploration of diffusion MRI, and related markers.

Conclusion

This study provides an in-depth overview of publications on MRI of WM in AD, identifying the current research status, hotspots, and frontier trends in the field.

Bridging patterns of neurocognitive aging across the older adult lifespan

Magnetic resonance imaging (MRI) studies of brain and neurocognitive aging rarely include oldest-old adults (ages 80 +). But predictions of neurocognitive aging theories derived from MRI findings in younger-old adults (ages ~55-80) may not generalize into advanced age, particularly given the increased prevalence of cognitive impairment/dementia in the oldest-old. Here, we reviewed the MRI literature in oldest-old adults and interpreted findings within the context of regional variation, compensation, brain maintenance, and reserve theories. Structural MRI studies revealed regional variation in brain aging as larger age effects on medial temporal and posterior regions for oldest-old than younger-old adults. They also revealed that brain maintenance explained preserved cognitive functioning into the tenth decade of life. Very few functional MRI studies examined compensatory activity in oldest-old adults who perform as well as younger groups, although there was evidence that higher brain reserve in oldest-old adults may mediate effects of brain aging on cognition. Despite some continuity, different cognitive and neural profiles across the older adult lifespan should be addressed in modern neurocognitive aging theories.

Neurovascular Ageing and Age-Related Diseases

Proper functioning of the brain is dependent on integrity of the cerebral vasculature. During ageing, a number of factors including aortic or arterial stiffness, autonomic dysregulation, neurovascular uncoupling and blood-brain barrier (BBB) damage will define the dynamics of brain blood flow and local perfusion. The nature and extent of ageing-related cerebrovascular changes, the degree of involvement of the heart and extracranial vessels and the consequent location of tissue pathology may vary considerably. Atheromatous disease retarding flow is a common vascular insult, which increases exponentially with increasing age. Arteriolosclerosis characterized as a prominent feature of small vessel disease is one of the first changes to occur during the natural history of cerebrovascular pathology. At the capillary level, the cerebral endothelium, which forms the BBB undergoes changes including reduced cytoplasm, fewer mitochondria, loss of tight junctions and thickened basement membranes with collagenosis. Astrocyte end-feet protecting the BBB retract as part of the clasmatodendrotic response whereas pericyte coverage is altered. The consequences of these microvascular changes are lacunar infarcts, cortical and subcortical microinfarcts, microbleeds and diffuse white matter disease, which involves myelin loss and axonal abnormalities. The deeper structures are particularly vulnerable because of the relatively reduced density of the microvascular network formed by perforating and penetrating end arteries. Ultimately, the integrity of both the neurovascular and gliovascular units is compromised such that there is an overall synergistic effect reflecting on ageing associated cerebral perfusion and permeability. More than one protagonist appears to be involved in ageing-related cognitive dysfunction characteristically associated with the neurocognitive disorders.

The pathology and pathophysiology of vascular dementia

Vascular dementia (VaD) is widely recognised as the second most common type of dementia. Consensus and accurate diagnosis of clinically suspected VaD relies on wide-ranging clinical, neuropsychological and neuroimaging measures in life but more importantly pathological confirmation. Factors defining subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes as well as time after the initial vascular event. Atherosclerotic and cardioembolic diseases combined appear the most common subtypes of vascular brain injury. In recent years, cerebral small vessel disease (SVD) has gained prominence worldwide as an important substrate of cognitive impairment. SVD is characterised by arteriolosclerosis, lacunar infarcts and cortical and subcortical microinfarcts and diffuse white matter changes, which involve myelin loss and axonal abnormalities. Global brain atrophy and focal degeneration of the cerebrum including medial temporal lobe atrophy are also features of VaD similar to Alzheimer's disease. Hereditary arteriopathies have provided insights into the mechanisms of dementia particularly how arteriolosclerosis, a major contributor of SVD promotes cognitive impairment. Recently developed and validated neuropathology guidelines indicated that the best predictors of vascular cognitive impairment were small or lacunar infarcts, microinfarcts, perivascular space dilation, myelin loss, arteriolosclerosis and leptomeningeal cerebral amyloid angiopathy. While these substrates do not suggest high specificity, VaD is likely defined by key neuronal and dendro-synaptic changes resulting in executive dysfunction and related cognitive deficits. Greater understanding of the molecular pathology is needed to clearly define microvascular disease and vascular substrates of dementia. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Parietal white matter lesions in Alzheimer's disease are associated with cortical neurodegenerative pathology, but not with small vessel disease

Cerebral white matter lesions (WML) encompass axonal loss and demyelination, and the pathogenesis is assumed to be small vessel disease (SVD)-related ischemia. However, WML may also result from the activation of Wallerian degeneration as a consequence of cortical Alzheimer's disease (AD) pathology, i.e. hyperphosphorylated tau (HPτ) and amyloid-beta (Aβ) deposition. WML seen in AD have a posterior predominance compared to non-demented individuals but it is unclear whether the pathological and molecular signatures of WML differ between these two groups. We investigated differences in the composition and aetiology of parietal WML from AD and non-demented controls. Parietal WML tissue from 55 human post-mortem brains (AD, n = 27; non-demented controls, n = 28) were quantitatively assessed for axonal loss and demyelination, as well as for cortical HPτ and Aβ burden and SVD. Biochemical assessment included Wallerian degeneration protease calpain and the myelin-associated glycoprotein (MAG) to proteolipid protein (PLP) ratio (MAG:PLP) as a measure of hypoperfusion. WML severity was associated with both axonal loss and demyelination in AD, but only with demyelination in controls. Calpain was significantly increased in WML tissue in AD, whereas MAG:PLP was significantly reduced in controls. Calpain levels were associated with increasing amounts of cortical AD-pathology but not SVD. We conclude that parietal WML seen in AD differ in their pathological composition and aetiology compared to WML seen in aged controls: WML seen in AD may be associated with Wallerian degeneration that is triggered by cortical AD-pathology, whereas WML in aged controls are due to ischaemia. Hence, parietal WML as seen on MRI should not invariably be interpreted as a surrogate biomarker for SVD as they may be indicative of cortical AD-pathology, and therefore, AD should also be considered as the main underlying cause for cognitive impairment in cases with parietal WML.

Neuropathological diagnosis of vascular cognitive impairment and vascular dementia with implications for Alzheimer's disease

Vascular dementia (VaD) is recognised as a neurocognitive disorder, which is explained by numerous vascular causes in the general absence of other pathologies. The heterogeneity of cerebrovascular disease makes it challenging to elucidate the neuropathological substrates and mechanisms of VaD as well as vascular cognitive impairment (VCI). Consensus and accurate diagnosis of VaD relies on wide-ranging clinical, neuropsychometric and neuroimaging measures with subsequent pathological confirmation. Pathological diagnosis of suspected clinical VaD requires adequate postmortem brain sampling and rigorous assessment methods to identify important substrates. Factors that define the subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes. Atherosclerotic and cardioembolic diseases appear the most common substrates of vascular brain injury or infarction. Small vessel disease characterised by arteriolosclerosis and lacunar infarcts also causes cortical and subcortical microinfarcts, which appear to be the most robust substrates of cognitive impairment. Diffuse WM changes with loss of myelin and axonal abnormalities are common to almost all subtypes of VaD. Medial temporal lobe and hippocampal atrophy accompanied by variable hippocampal sclerosis are also features of VaD as they are of Alzheimer’s disease. Recent observations suggest that there is a vascular basis for neuronal atrophy in both the temporal and frontal lobes in VaD that is entirely independent of any Alzheimer pathology. Further knowledge on specific neuronal and dendro-synaptic changes in key regions resulting in executive dysfunction and other cognitive deficits, which define VCI and VaD, needs to be gathered. Hereditary arteriopathies such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy or CADASIL have provided insights into the mechanisms of dementia associated with cerebral small vessel disease. Greater understanding of the neurochemical and molecular investigations is needed to better define microvascular disease and vascular substrates of dementia. The investigation of relevant animal models would be valuable in exploring the pathogenesis as well as prevention of the vascular causes of cognitive impairment.

White matter hyperintensities are more highly associated with preclinical Alzheimer's disease than imaging and cognitive markers of neurodegeneration

INTRODUCTION

Cognitive tests and nonamyloid imaging biomarkers do not consistently identify preclinical AD. The objective of this study was to evaluate whether white matter hyperintensity (WMH) volume, a cerebrovascular disease marker, is more associated with preclinical AD than conventional AD biomarkers and cognitive tests.

METHODS

Elderly controls enrolled in the Alzheimer's Disease Neuroimaging Initiative (ADNI, n = 158) underwent florbetapir-PET scans, psychometric testing, neuroimaging with MRI and PET, and APOE genetic testing. Elderly controls the Parkinson's progression markers initiative (PPMI, n = 58) had WMH volume, cerebrospinal fluid (CSF) Aβ1-42, and APOE status measured.

RESULTS

In the ADNI cohort, only WMH volume and APOE ε4 status were associated with cerebral Aβ (standardized β = 0.44 and 1.25, P = .03 and .002). The association between WMH volume and APOE ε4 status with cerebral Aβ (standardized β = 1.12 and 0.26, P = .048 and .045) was confirmed in the PPMI cohort.

DISCUSSION

WMH volume is more highly associated with preclinical AD than other AD biomarkers.

Stroke injury, cognitive impairment and vascular dementia

The global burden of ischaemic strokes is almost 4-fold greater than haemorrhagic strokes. Current evidence suggests that 25–30% of ischaemic stroke survivors develop immediate or delayed vascular cognitive impairment (VCI) or vascular dementia (VaD). Dementia after stroke injury may encompass all types of cognitive disorders. States of cognitive dysfunction before the index stroke are described under the umbrella of pre-stroke dementia, which may entail vascular changes as well as insidious neurodegenerative processes. Risk factors for cognitive impairment and dementia after stroke are multifactorial including older age, family history, genetic variants, low educational status, vascular comorbidities, prior transient ischaemic attack or recurrent stroke and depressive illness. Neuroimaging determinants of dementia after stroke comprise silent brain infarcts, white matter changes, lacunar infarcts and medial temporal lobe atrophy. Until recently, the neuropathology of dementia after stroke was poorly defined. Most of post-stroke dementia is consistent with VaD involving multiple substrates. Microinfarction, microvascular changes related to blood–brain barrier damage, focal neuronal atrophy and low burden of co-existing neurodegenerative pathology appear key substrates of dementia after stroke injury. The elucidation of mechanisms of dementia after stroke injury will enable establishment of effective strategy for symptomatic relief and prevention. Controlling vascular disease risk factors is essential to reduce the burden of cognitive dysfunction after stroke. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

•

Ischaemic injury is common among long-term stroke survivors

•

About 25% stroke survivors develop dementia with a much greater proportion developing cognitive impairment

•

Risk factors of dementia after stroke include older age, vascular comorbidities, prior stroke and pre-stroke impairment

•

Current imaging and pathological studies suggest 70% of dementia after stroke is vascular dementia

•

Severe white matter changes and medial temporal lobe atrophy as sequelae after ischaemic injury are substrates of dementia

•

Controlling vascular risk factors and prevention strategies related to lifestyle factors would reduce dementia after stroke

White matter integrity, hippocampal volume, and cognitive performance of a world-famous nonagenarian track-and-field athlete

Physical activity (PA) and cardiorespiratory fitness (CRF) are associated with successful brain and cognitive aging. However, little is known about the effects of PA, CRF, and exercise on the brain in the oldest-old. Here we examined white matter (WM) integrity, measured as fractional anisotropy (FA) and WM hyperintensity (WMH) burden, and hippocampal (HIPP) volume of Olga Kotelko (1919-2014). Olga began training for competitions at age of 77 and as of June 2014 held over 30 world records in her age category in track-and-field. We found that Olga's WMH burden was larger and the HIPP was smaller than in the reference sample (58 healthy low-active women 60-78 years old), and her FA was consistently lower in the regions overlapping with WMH. Olga's FA in many normal-appearing WM regions, however, did not differ or was greater than in the reference sample. In particular, FA in her genu corpus callosum was higher than any FA value observed in the reference sample. We speculate that her relatively high FA may be related to both successful aging and the beneficial effects of exercise in old age. In addition, Olga had lower scores on memory, reasoning and speed tasks than the younger reference sample, but outperformed typical adults of age 90-95 on speed and memory. Together, our findings open the possibility of old-age benefits of increasing PA on WM microstructure and cognition despite age-related increase in WMH burden and HIPP shrinkage, and add to the still scarce neuroimaging data of the healthy oldest-old (>90 years) adults.

Metabolic syndrome and cerebrovascular impairment in Alzheimer's disease

OBJECTIVE

Metabolic Syndrome (MeS) has inconstantly been associated with cognitive impairment. The aim of this study was to investigate the influence of MeS on cerebrovascular reactivity and the possible consequences on cognitive impairment in patients with Alzheimer's disease (AD).

METHODS

A total of 162 AD patients were enrolled and grouped depending on the presence/absence of MeS. An ultrasound assessment of the neck vessels was performed to evaluate common carotid artery intima-media thickness (IMT). Cerebral hemodynamics was assessed by the transcranial Doppler-based breath-holding index (BHI) test. The relationship between BHI and MeS was explored first with a nested binary logistic model and then with a general linear model/adjusted model. Both models were corrected for sex, age, education, BMI, smoking attitude, and IMT treated as covariates.

RESULTS

Pathologic BHI values were significantly more frequent among patients with MeS (risk ratio (RR):1.477; 95% CI: 1.177-1.848). MeS significantly improved the prediction of a pathologic BHI in the binary logistic model (odds ratio (OR):11.64; 95% CI: 1.001-135.304; p < 0.05). Moreover, AD patients affected by MeS had significantly lower mean Mini-Mental State Evaluation values than the unaffected ones (16.06; 95% CI: 14.96-17.15 vs 17.79; 95% CI: 17.05-18.53; p < 0.0001).

CONCLUSIONS

Our data show an association between the presence of MeS and cerebral hemodynamics. The possibility that a cluster of potentially treatable vascular risk factors may influence AD patients' prognosis deserves consideration.

Prevalence of mixed pathologies in the aging brain

The spectrum of mixed brain pathologies expands beyond accompanying vascular pathology in brains with Alzheimer's disease-related pathology. Co-occurrence of neurodegenerative non-Alzheimer's disease-type proteinopathies is increasingly recognized to be a frequent event in the brains of symptomatic and asymptomatic patients, particularly in older people. Owing to the evolving concept of neurodegenerative diseases, clinical and neuropathological diagnostic criteria have changed during the last decades. Autopsy-based studies differ in the selection criteria and also in the applied staining methods used. The present review summarizes the prevalence of mixed brain pathologies reported in recent community-based studies. In these cohorts, irrespective of the clinical symptoms, the frequency of Alzheimer's disease-related pathology is between 19 and 67%, of Lewy body pathology is between 6 and 39%, of vascular pathologies is between 28 and 70%, of TDP-43 proteinopathy is between 13 and 46%, of hippocampal sclerosis is between 3 and 13% and, finally, of mixed pathologies is between 10 and 74%. Some studies also mention tauopathies. White-matter pathologies are not discussed specifically in all studies, although these lesions may be present in more than 80% of the aging brains. In summary, community-based neuropathology studies have shown that complex constellations of underlying pathologies may lead to cognitive decline, and that the number of possible combinations increases in the aging brain. These observations have implications for the prediction of the prognosis, for the development of biomarkers or therapy targets, or for the stratification of patient cohorts for genome-wide studies or, eventually, for therapy trials.

Cognitive impairment and risk of future stroke: a systematic review and meta-analysis

BACKGROUND

Several studies have assessed the link between cognitive impairment and risk of future stroke, but results have been inconsistent. We conducted a systematic review and meta-analysis of cohort studies to determine the association between cognitive impairment and risk of future stroke.

METHODS

We searched MEDLINE and Embase (1966 to November 2013) and conducted a manual search of bibliographies of relevant retrieved articles and reviews. We included cohort studies that reported multivariable adjusted relative risks and 95% confidence intervals or standard errors for stroke with respect to baseline cognitive impairment.

RESULTS

We identified 18 cohort studies (total 121 879 participants) and 7799 stroke events. Pooled analysis of results from all studies showed that stroke risk increased among patients with cognitive impairment at baseline (relative risk [RR] 1.39, 95% confidence interval [CI] 1.24-1.56). The results were similar when we restricted the analysis to studies that used a widely adopted definition of cognitive impairment (i.e., Mini-Mental State Examination score < 25 or nearest equivalent) (RR 1.64, 95% CI 1.46-1.84). Cognitive impairment at baseline was also associated with an increased risk of fatal stroke (RR 1.68, 95% CI 1.21-2.33) and ischemic stroke (RR 1.65, 95% CI 1.41-1.93).

INTERPRETATION

Baseline cognitive impairment was associated with a significantly higher risk of future stroke, especially ischemic and fatal stroke.