Plasma beta amyloid and impaired CO2-induced cerebral vasomotor reactivity

Amyloid beta (Abeta) may disturb cerebral autoregulation by damaging the wall of small cerebral blood vessels and by direct negative vasoactive properties. We assessed whether previous and concurrent plasma Abeta(1-40) and Abeta(1-42) levels were associated with an impaired CO2-induced cerebral vasomotor response. In the longitudinal population-based Rotterdam Study we measured plasma Abeta levels and cerebral vasomotor reactivity to hypercapnia with transcranial Doppler ultrasonography (TCD) in 441 people, aged 60-90 years. We performed age and sex adjusted logistic regression analysis. Plasma Abeta levels assessed on average 6.5-year before TCD were linearly associated with an impaired CO2-induced cerebral vasomotor response (odds ratio 1.48 (95%CI 1.19;1.84) per standard deviation increase in Abeta(1-40), and 1.36 (95%CI 1.09;1.70) per standard deviation increase in Abeta(1-42)). Such an association was not present for Abeta assessed concurrently with the TCD measurement. Persons whose plasma Abeta(1-40) levels had decreased in the 6.5-year period preceding TCD measurements were more likely to have an impaired CO2-induced vasomotor reactivity. Overall our observations are most compatible with plasma Abeta levels representing vascular Abeta deposits years later resulting in impaired CO2-induced vasomotor reactivity.

MR spectroscopy of brain white matter in the prediction of dementia

BACKGROUND

Previous 1H-MR spectroscopy (MRS) studies compared biochemical spectra of persons with dementia with those of healthy control subjects. Given the long prodromal period of Alzheimer disease (AD), the authors sought to investigate whether biochemical changes can be observed also in the preclinical period.

METHODS

The authors prospectively followed 509 elderly persons (ages 60 to 90), who were free of clinical dementia at baseline, for on average 5.9 years. At baseline, 1H-MRS of the brain (1.5 T) was performed in a plane above the lateral ventricles that comprised mainly white matter voxels. Standard ratios of N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) were calculated. Structural MRI was administered to assess white matter lesions and hippocampal atrophy. All persons were followed for incident dementia through repeated neuropsychological testing and linkage with medical records.

RESULTS

During follow-up, 37 persons developed dementia, of whom 27 fulfilled criteria for AD. Overall, biochemical ratios on 1H-MRS at baseline were not associated with the risk of incident dementia. However, people with higher Cho/Cr ratios had a higher risk to develop dementia or AD within 4 years (hazard ratio for dementia per SD increase 1.55 [95% CI 1.05 to 2.28]). This association attenuated and became nonsignificant after adjustment for white matter lesions on MRI.

CONCLUSION

These data suggest that there are biochemical changes on 1H-MR spectroscopy of brains of persons with presymptomatic dementia.

Retinal vessel diameters and cerebral small vessel disease: the Rotterdam Scan Study

The direct visualization of retinal vessels provides a unique opportunity to study cerebral small vessel disease, because these vessels share many features. It was reported that persons with smaller retinal arteriolar-to-venular ratio tended to have more white matter lesions on MRI. It is unclear whether this is due to arteriolar narrowing or venular dilatation. We investigated whether smaller arteriolar or larger venular diameters or both were related to severity and progression of cerebral small vessel disease. We studied 490 persons (60-90 years) without dementia from a population-based cohort study. At baseline (1990-1993), retinal arteriolar and venular diameters were measured on digitized images of one eye of each participant. In 1995-1996, participants underwent cerebral MRI scanning. We rated the severity of periventricular white matter lesions on a 9-point scale, approximated a total subcortical white matter lesion volume (range: 0-29.5 ml) and rated the presence of lacunar infarcts. On average 3.3 years later, 279 persons had a second MRI. Changes in periventricular and subcortical white matter lesions were rated with a semi-quantitative scale, and progression was classified as no, minor and marked. An incident infarct was a new infarct on the follow-up MRI. Neither venular nor arteriolar diameters were related to the severity of cerebral small vessel disease. Larger venular diameters were, however, associated with a marked progression of cerebral small vessel disease. Age and gender adjusted odds ratios (ORs) per standard deviation increase were 1.71 [95% confidence interval (CI): 1.11-2.61] for periventricular, 1.72 (95% CI: 1.09-2.71) for subcortical white matter lesion progression and 1.59 (95% CI: 1.06-2.39) for incident lacunar infarcts. These associations were independent of other cardiovascular risk factors. Only the OR for incident lacunar infarcts was attenuated (1.24; 95% CI: 0.72-2.12). No association was observed between arteriolar diameters and progression of cerebral small vessel disease. In conclusion, retinal venular dilatation was related to progression of cerebral small vessel disease. The mechanisms underlying venular dilatation deserve more attention, as they may provide new clues into the pathophysiology of cerebral small vessel disease.

Association between blood pressure, white matter lesions, and atrophy of the medial temporal lobe

BACKGROUND

Blood pressure level is associated with the risk of clinical Alzheimer disease (AD), yet the underlying mechanisms are unclear. High blood pressure levels may cause cerebral small-vessel pathology, which contributes to cognitive decline in patients with AD. Alternatively, in persons with high blood pressure, increased numbers of neurofibrillary tangles and amyloid plaques at autopsy have also been observed, suggesting direct links between blood pressure and AD.

OBJECTIVE

To investigate the association of blood pressure and markers of small-vessel disease (white matter lesions [WMLs] on MRI) with hippocampal and amygdalar atrophy on MRI-potential in vivo indicators of Alzheimer pathology.

METHODS

In 1995 to 1996, 511 nondemented elderly subjects (age 60 to 90) underwent MRI. The extent of WMLs was assessed, and volumes of the hippocampus and amygdala were measured. Blood pressure levels were assessed at the time of MRI and 5 years before the MRI.

RESULTS

Higher diastolic blood pressure 5 years before MRI predicted more hippocampal atrophy in persons untreated for hypertension (per SD increase -0.10 mL [95% CI -0.19 to -0.02, p = 0.02]). Conversely, in persons treated for hypertension, a low diastolic blood pressure was associated with more severe atrophy. Persons with more WMLs on MRI more often had severe atrophy of the hippocampus and amygdala.

CONCLUSION

Blood pressure and indicators of small-vessel disease in the brain may be associated with atrophy of structures affected by Alzheimer pathology.

C-Reactive Protein and Cerebral Small-Vessel Disease

Background— Inflammatory processes are involved in the development and consequences of atherosclerosis. Whether these processes are also involved in cerebral small-vessel disease is unknown. Cerebral white matter lesions and lacunar brain infarcts are caused by small-vessel disease and are commonly observed on MRI scans in elderly people. These lesions are associated with an increased risk of stroke and dementia. We assessed whether higher C-reactive protein (CRP) levels were related to white matter lesion and lacunar infarcts.

Methods and Results— We based our study on 1033 participants of the population-based Rotterdam Scan Study for whom complete data on CRP levels were available and who underwent brain MRI scanning. Subjects were 60 to 90 years of age and free of dementia at baseline. Six hundred thirty-six subjects had a second MRI scan on average 3.3 years later. We used multivariate regression models to assess the associations between CRP levels and markers of small-vessel disease. Higher CRP levels were associated with presence and progression of white matter lesions, particularly with marked lesion progression (ORs for highest versus lowest quartile of CRP 3.1 [95% CI 1.3 to 7.2] and 2.5 [95% CI 1.1 to 5.6] for periventricular and subcortical white matter lesion progression, respectively). These associations persisted after adjustment for cardiovascular risk factors and carotid atherosclerosis. Persons with higher CRP levels tended to have more prevalent and incident lacunar infarcts.

Conclusions— Inflammatory processes may be involved in the pathogenesis of cerebral small-vessel disease, in particular, the development of white matter lesions.

Cerebral small-vessel disease and decline in information processing speed, executive function and memory

Cerebral small-vessel disease is common in older people and may contribute to the development of dementia. The objective of the present study was to evaluate the relationship between measures of cerebral small-vessel disease on MRI and the rate of decline in specific cognitive domains in participants from the prospective, population-based Rotterdam Scan Study. Participants were 60-90 years of age and free from dementia at baseline in 1995-1996. White matter lesions (WML), cerebral infarcts and generalized brain atrophy were assessed on the baseline MRI. We performed neuropsychological testing at baseline and repeatedly in 1999-2000 and in 2001-2003. We used random-effects models for repeated measures to examine the association between quantitative MRI measures and rate of decline in measures of global cognitive function, information processing speed, executive function and memory. There were a total of 2266 assessments for the 832 participants in the study, with an average time from the initial to last assessment of 5.2 years. Increasing severity of periventricular WML and generalized brain atrophy and the presence of brain infarcts on MRI were associated with a steeper decline in cognitive function. These structural brain changes were specifically associated with decline in information processing speed and executive function. The associations between MRI measures of cerebral small-vessel disease and cognitive decline did not change after additional adjustment for vascular risk factors or depressed mood. After exclusion of participants with an incident stroke, some of the associations of periventricular WML, brain infarcts and generalized brain atrophy with measures of information processing speed and executive function were no longer significant. This may indicate that stroke plays an intermediate role in the relationship between cerebral small-vessel disease and cognitive decline. Our results suggest that in older people cerebral small-vessel disease may contribute to cognitive decline by affecting information processing speed and executive function.

Cerebral white matter lesions and the risk of dementia

OBJECTIVE

To study the association between white matter lesions (WML) in specific locations and the risk of dementia.

DESIGN

The Rotterdam Scan Study, a prospective population-based cohort study. We scored periventricular and subcortical WML on magnetic resonance imaging and observed participants until January 2002 for incident dementia.

SETTING

General population.

PARTICIPANTS

We included 1077 people aged 60 to 90 years who did not have dementia at baseline.

MAIN OUTCOME MEASURE

Incident dementia by Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM III-R) criteria.

RESULTS

During a mean follow-up of 5.2 years, 45 participants developed dementia. Higher severity of periventricular WML increased the risk of dementia, whereas the association between subcortical WML and dementia was less prominent. The adjusted hazard ratio of dementia for each standard deviation increase in periventricular WML severity was 1.67 (95% confidence interval, 1.25-2.24). This increased risk was independent of other risk factors for dementia and partly independent of other structural brain changes on magnetic resonance imaging.

CONCLUSION

White matter lesions, especially in the periventricular region, increase the risk of dementia in elderly people.

Alcohol intake in relation to brain magnetic resonance imaging findings in older persons without dementia

BACKGROUND

Consumers of light-to-moderate amounts of alcohol have a lower risk of dementia and, possibly, Alzheimer disease than do abstainers. Because vascular disease may contribute to symptoms of Alzheimer disease, reduction of cerebrovascular disease in consumers of light amounts of alcohol could account for that observation. However, a low concentration of alcohol may also have direct effects on the hippocampus, a brain structure highly affected by Alzheimer disease.

OBJECTIVE

We investigated alcohol intake in relation to brain magnetic resonance imaging (MRI) findings of presumed vascular origin (ie, white matter lesions and infarcts) and findings more specifically found in early Alzheimer disease (ie, hippocampal and amygdalar atrophy).

DESIGN

In a population-based sample of 1074 older persons without dementia (aged 60-90 y), we made brain MRIs from which we rated white matter lesions and brain infarcts. In a subset of 509 people, hippocampal and amygdalar volumes on MRI were measured. Alcohol intake was assessed by using a structured questionnaire. We categorized alcohol intake as lifetime abstention and very light (<1 drink/wk), light (>/=1 drink/wk to <1 drink/d), moderate (>/=1 drink/d to <4 drinks/d), and heavy (>/=4 drinks/d) intakes.

RESULTS

Persons whose alcohol consumption was light to moderate had less severe white matter lesions and brain infarcts on MRI than did abstainers or heavy drinkers. Abstainers and very light drinkers had smaller hippocampal and amygdalar volumes on MRI than did light-to-moderate drinkers, but only if the former carried an apolipoprotein (APOE) epsilon4 allele.

CONCLUSION

Light-to-moderate alcohol intake is associated with a lower prevalence of vascular brain findings and, in APOE epsilon4 carriers, hippocampal and amygdalar atrophy on MRI.

Neuroanatomical localisation and clinical correlates of white matter lesions in the elderly

BACKGROUND

White matter lesions (WML) in elderly people co-occur with hypertension, depression, and cognitive impairment. Little is known about the density and distribution of WML in normal elderly people, whether they occur randomly in the aging brain or tend to cluster in certain areas, or whether patterns of WML aggregation are linked to clinical symptoms.

OBJECTIVES

To describe patterns of WML distribution in a large representative population of elderly people using non-inferential cluster analysis; and to determine the extent to which such patterns are associated with clinical symptomatology.

METHOD

A population sample of 1077 elderly people was recruited. Multiple analysis of correspondence followed by automatic classification methods was used to explore overall patterns of WML distribution. Correspondence was then sought between these patterns and a range of cerebrovascular, psychiatric, and neurological symptoms.

RESULTS

Three distinct patterns of spatial localisation within the brain were observed, corresponding to distinct clusters of clinical symptoms. In particular WML aggregation in temporal and occipital areas was associated with greater age, hypertension, late onset depressive disorder, poor global cognitive function, and overall WML frequency.

CONCLUSIONS

WML localisation is not random in the aging brain, and their distribution is associated with age and the presence of clinical symptoms. Age differences suggest there may be patterns of progression across time; however, this requires confirmation from longitudinal imaging studies.

Measuring progression of cerebral white matter lesions on MRI

OBJECTIVE

To evaluate the concordance of a volumetric method for measuring white matter lesion (WML) change with visual rating scales.

METHODS

The authors selected a stratified sample of 20 elderly people (mean age 72 years, range 61 to 88 years) with an MRI examination at baseline and at 3-year follow-up from the community-based Rotterdam Scan Study (RSS). Four raters assessed WML change with four different visual rating scales: the Fazekas scale, the Scheltens scale, the RSS scale, and a new visual rating scale that was designed to measure change in WML. The authors assessed concordance with a volumetric method with scatter plots and correlations, and interobserver agreement with intraclass correlation coefficients.

RESULTS

For assessment of change in WML, the Fazekas, Scheltens, and periventricular part of the RSS scale showed little correlation with volumetrics, and low interobserver agreement. The authors' new WML change scale and the subcortical part of the RSS scale showed good correlation with volumetrics. After additional training, the new WML change scale showed good interobserver agreement for measuring WML change.

CONCLUSIONS

Commonly used visual rating scales are not well suited for measuring change in white matter lesion severity. The authors' new white matter lesion change scale is more accurate and precise, and may be of use in studies focusing on progression of white matter lesions.

Arterial oxygen saturation, COPD, and cerebral small vessel disease

OBJECTIVE

To study whether lower arterial oxygen saturation (SaO(2)) and chronic obstructive pulmonary disease (COPD) are associated with cerebral white matter lesions and lacunar infarcts.

METHODS

We measured SaO(2) twice with a pulse oximeter, assessed the presence of COPD, and performed MRI in 1077 non-demented people from a general population (aged 60-90 years). We rated periventricular white matter lesions (on a scale of 0-9) and approximated a total subcortical white matter lesion volume (range 0-29.5 ml). All analyses were adjusted for age and sex and additionally for hypertension, diabetes, body mass index, pack years smoked, cholesterol, haemoglobin, myocardial infarction, and left ventricular hypertrophy.

RESULTS

Lower SaO(2) was independent of potential confounders associated with more severe periventricular white matter lesions (score increased by 0.12 per 1% decrease in SaO(2) (95% confidence interval 0.01 to 0.23)). Participants with COPD had more severe periventricular white matter lesions than those without (adjusted mean difference in score 0.70 (95% confidence interval 0.23 to 1.16)). Lower SaO(2) and COPD were not associated with subcortical white matter lesions or lacunar infarcts.

CONCLUSION

Lower SaO(2) and COPD are associated with more severe periventricular white matter lesions.

Plasma amyloid ?, apolipoprotein E, lacunar infarcts, and white matter lesions

Lacunar brain infarcts and cerebral white matter lesions are frequently observed on magnetic resonance imaging scans in elderly subjects. These lesions are also frequent in patient with cerebral amyloid angiopathy. We examined whether plasma amyloid beta peptide (Abeta) levels are associated with lacunar infarcts and white matter lesions in the general population, and whether the apolipoprotein E (APOE) genotype modifies these associations. We studied 1,077 participants within the population-based Rotterdam Scan Study, who were 60 to 90 years of age and free of dementia. Cross-sectional associations were analyzed by regression models with adjustments for age, sex, creatinine levels, and hypertension. In APOE epsilon4 carriers, plasma Abeta levels were positively associated with lacunar infarcts and white matter lesions, whereas in noncarriers no associations were observed. Per standard deviation increase in Abeta(1-40) and Abeta(1-42) levels the odds ratios for lacunar infarcts were 1.72 (95% confidence interval [CI] = 1.22-2.43) and 1.93 (95% CI = 1.31-2.85), the periventricular white matter lesion grade increased by 0.32 (95% CI = 0.08-0.57) and 0.29 (95% CI = 0.00-0.57), and the subcortical white matter lesion volume increased by 0.48 ml (95% CI = 0.04-0.91) and 0.24 ml (95% CI = -0.27-0.75). Higher Abeta levels are associated with more lacunar infarcts and white matter lesions in elderly subjects who carry an APOE epsilon4 allele.

Type 2 diabetes and atrophy of medial temporal lobe structures on brain MRI

AIM/HYPOTHESIS

Type 2 diabetes increases the risk not only of vascular dementia but also of Alzheimer's disease. The question remains whether diabetes increases the risk of Alzheimer's disease by diabetic vasculopathy or whether diabetes influences directly the development of Alzheimer neuropathology. In vivo, hippocampal and amygdalar atrophy on brain MRI are good, early markers of the degree of Alzheimer neuropathology. We investigated the association between diabetes mellitus, insulin resistance and the degree of hippocampal and amygdalar atrophy on magnetic resonance imaging (MRI) accounting for vascular pathology.

METHODS

Data was obtained in a population-based study of elderly subjects without dementia between 60 to 90 years of age. The presence of diabetes mellitus and, in non-diabetic subjects, insulin resistance was assessed for 506 participants in whom hippocampal and amygdalar volumes on MRI were measured. We assessed the degree of vascular morbidity by rating carotid atherosclerosis, and brain white matter lesions and infarcts on MRI.

RESULTS

Subjects with diabetes mellitus had more hippocampal and amygdalar atrophy on MRI compared to subjects without diabetes mellitus. Furthermore, increasing insulin resistance was associated with more amygdalar atrophy on MRI. The associations were not due to vascular morbidity being more pronounced in persons with diabetes mellitus.

CONCLUSIONS/INTERPRETATION

Type 2 diabetes is associated with hippocampal and amygdalar atrophy, regardless of vascular pathology. This could suggest that Type 2 diabetes directly influences the development of Alzheimer neuropathology.

Operational definitions for the NINDS-AIREN criteria for vascular dementia: an interobserver study

BACKGROUND AND PURPOSE

Vascular dementia (VaD) is thought to be the most common cause of dementia after Alzheimer's disease. The commonly used International Workshop of the National Institute of Neurological Disorders and Stroke (NINDS) and the Association Internationale pour la Recherche et l'Enseignement en Neurosciences (AIREN) criteria for VaD necessitate evidence of vascular disease on CT or MRI of the brain. The purposes of our study were to operationalize the radiological part of the NINDS-AIREN criteria and to assess the effect of this operationalization on interobserver agreement.

METHODS

Six experienced and 4 inexperienced observers rated a set of 40 MRI studies of patients with clinically suspected VaD twice using the NINDS-AIREN set of radiological criteria. After the first reading session, operational definitions were conceived, which were subsequently used in the second reading session. Interobserver reproducibility was measured by Cohen's kappa.

RESULTS

Overall agreement at the first reading session was poor (kappa=0.29) and improved slightly after application of the additional definitions (kappa=0.38). Raters in the experienced group improved their agreement from almost moderate (kappa=0.39) to good (0.62). The inexperienced group started out with poor agreement (kappa=0.17) and did not improve (kappa=0.18). The experienced group improved in both the large- and small-vessel categories, whereas the inexperienced group improved generally in the extensive white matter hyperintensities categories.

CONCLUSIONS

Considerable interobserver variability exists for the assessment of the radiological part of the NINDS-AIREN criteria. Use of operational definitions improves agreement but only for already experienced observers.

Silent brain infarcts and the risk of dementia and cognitive decline

BACKGROUND

Silent brain infarcts are frequently seen on magnetic resonance imaging (MRI) in healthy elderly people and may be associated with dementia and cognitive decline.

METHODS

We studied the association between silent brain infarcts and the risk of dementia and cognitive decline in 1015 participants of the prospective, population-based Rotterdam Scan Study, who were 60 to 90 years of age and free of dementia and stroke at base line. Participants underwent neuropsychological testing and cerebral MRI at base line in 1995 to 1996 and again in 1999 to 2000 and were monitored for dementia throughout the study period. We performed Cox proportional-hazards and multiple linear-regression analyses, adjusted for age, sex, and level of education and for the presence or absence of subcortical atrophy and white-matter lesions.

RESULTS

During 3697 person-years of follow-up (mean per person, 3.6 years), dementia developed in 30 of the 1015 participants. The presence of silent brain infarcts at base line more than doubled the risk of dementia (hazard ratio, 2.26; 95 percent confidence interval, 1.09 to 4.70). The presence of silent brain infarcts on the base-line MRI was associated with worse performance on neuropsychological tests and a steeper decline in global cognitive function. Silent thalamic infarcts were associated with a decline in memory performance, and nonthalamic infarcts with a decline in psychomotor speed. When participants with silent brain infarcts at base line were subdivided into those with and those without additional infarcts at follow-up, the decline in cognitive function was restricted to those with additional silent infarcts.

CONCLUSIONS

Elderly people with silent brain infarcts have an increased risk of dementia and a steeper decline in cognitive function than those without such lesions.

Frequency of white matter lesions and silent lacunar infarcts

White matter lesions and silent lacunar infarcts are related to and may result from cerebral small vessel disease. Reported frequencies of these lesions vary largely among studies. Differences in imaging techniques, rating scales, cut-off points in lesion severity grading and study populations contribute to the variation, in addition to differences in risk factor profiles across studies. In this paper, we will firstly discuss general methodological issues that may influence reported frequencies of white matter lesions and silent lacunar infarctions, and then review published data. We will focus on the results from population-based studies and only briefly comment on patient series of stroke and dementia.

Homocysteine and cognitive function in the elderly: the Rotterdam Scan Study

BACKGROUND

Elevated plasma total homocysteine (tHcy) concentrations are associated with AD and vascular dementia, but the relation with cognitive performance in nondemented elderly people is not known.

OBJECTIVE

To examine the association of tHcy and cognitive function in the elderly, and assess whether this may be mediated by structural brain changes on MRI.

METHODS

The Rotterdam Scan Study is a population-based study of 1,077 nondemented elderly. Cognitive performance was assessed, and compound scores were constructed for psychomotor speed, memory function, and global cognitive function. Cerebral infarcts, white matter lesions, and generalized brain atrophy were measured on MRI. The cross-sectional relationship between tHcy levels and neuropsychological test scores was assessed by multiple regression.

RESULTS

Mean tHcy level was 11.5 micro mol/L (SD 4.1). Increasing tHcy levels were associated with lower scores for psychomotor speed, memory function, and global cognitive function, and this was largely due to the association with tHcy levels in the upper quintile (>14 micro mol/L). Adjusted differences between test scores of participants in the upper quintile as compared with the lower four quintiles of tHcy were -0.26 (95% CI: -0.37; -0.14) for psychomotor speed, -0.13 (95% CI: -0.27; 0.01) for memory function, and -0.20 (95% CI: -0.30; -0.11) for global cognitive function. These associations were not mediated by structural brain changes on MRI.

CONCLUSION

Elevated tHcy levels are associated with decreased cognitive performance in nondemented elderly people, and the relation was most marked for psychomotor speed. This association was independent of structural brain changes on MRI.