White matter changes: the clinical consequences in the aging population

White Matter Language Pathways and Language Performance in Healthy Adults Across Ages

The goal of this study was to determine the relationship between age-related white matter changes, with a specific focus on previously identified language pathways, and language functioning in healthy aging. 228 healthy participants (126 female; 146 right-handed), ages 18 to 76, underwent 3.0 Tesla MR diffusion weighted imaging (DWI) and a battery of language assessments including the Boston Naming Test (BNT), the Peabody Picture Vocabulary Test (PPVT), the Controlled Oral Word Association Test (COWAT), Semantic Fluency Test (SFT), and a subset of the Boston Diagnostic Aphasia Examination (CI-BDAE). Using tract based spatial statistics (TBSS), we investigated measurements of fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD). TBSS was used to create a white matter skeleton that was then used to analyze white matter changes (indexed by FA, AD, RD, and MD) with age and language performance. Results focused primarily on significant relationships (p < 0.05, cluster-wise FDR corrected for multiple comparisons) in the canonical language white matter pathways. We found a diffuse linear decrease with age in global white matter FA and a significant focal increase in FA with age within the bilateral superior cerebellar peduncles (SCPs). We observed that increased BNT scores were associated with increased FA within the left SLF, and within the posterior and antero-lateral portions of the right inferior frontal-occipital fasciculus (IFOF). Increased SFT and PPVT scores were associated with increased FA within the posterior portion of the right IFOF and increased FA within the left body of the corpus callosum was associated with lower COWAT scores. We found no association between FA and BDAE. MD, RD, and AD, were found to be inversely proportional to FA within the IFOF, with AD showing a negative correlation with SFT, and RD and MD showing a negative correlation with BNT. There was no association between CI-BDAE and any of the white matter measures. Significant differences between sexes included more pronounced FA decrease with age within the right SLF in males vs. females; there were no differences in language performance scores between sexes. We also found that there was no decline in language testing scores with increasing age in our cohort. Taken together, our findings of varying relationships between DTI metrics and language function within multiple regions of the non-dominant IFOF suggest that more robust language networks with bilateral structural connectivity may contribute to better overall language functioning, regardless of age.

White matter hyperintensities and medication adherence

White matter hyperintensities (WMH) are associated with hypertension, age, and cognitive function, but the association between WMH and medication adherence has not been examined. The intent of this investigation was to consider the potential implications of hypertension-related brain morphological changes on medication adherence and thereby improve understanding of the self-management consequences of hypertension. The associations between WMH, blood pressure, age, cognitive function (specifically assessments of prefrontal function), and medication adherence were examined in 16 middle-aged and older adults self-managing at least one prescribed antihypertensive agent. Magnetic resonance imaging using an axial fluid attenuated inversion recovery (FLAIR) sequence was used to assess the presence of WMH. Cognitive assessments included measures of executive function, working memory, attention, and immediate recall. Adherence was monitored for 8 weeks using electronic medication monitoring. More WMH were associated with poorer adherence (rs = -.25) and with higher systolic blood pressure (rs = .46), although these relationships were not statistically significant. WMH were associated with cognitive assessments in the expected direction including Digit Span Backward (rs = -.53, p < .05). Adherence was associated with immediate memory (rs = .54, p < .05) and inversely associated with failure to maintain set on the Wisconsin Card Sorting Test (WCST; rs = -.61, p < .05). These findings provide preliminary evidence for the association between WMH, assessments of prefrontal function, and medication adherence.

Potential surrogate markers of cerebral microvascular angiopathy in asymptomatic subjects at risk of stroke

Cerebral microvascular angiopathy (MVA) is associated with clinical vascular risk factors and is characterised by histological changes, including thickening of the walls of arterial vessels and dilatation of the Virchow-Robin spaces (VRS). We have previously described two novel biomarkers of MVA based on magnetic resonance imaging (MRI), VRS dilatation and abnormalities in the transfer of systolic arterial pulsation to the ventricular CSF, which occur as a result of decreased cerebral arterial compliance. These are associated with vascular dementia and treatment-resistant late onset depression. We studied a group of normal subjects at risk of cerebrovascular disease to determine if these biomarkers are present in patients who have no evidence of symptomatic vascular disease. We studied 31 subjects, 16 with three or more vascular risk factors and 15 with one or less significant risk factors. We measured arterial blood flow and CSF flow in the cerebral aqueduct, white matter lesion load, and the distribution and number of VRS. There were significant differences in CSF pulsatility and in VRS in the basal ganglia between the two groups, but no differences in white matter lesion load. We conclude that asymptomatic subjects at risk of stroke have MRI evidence of MVA before white matter lesions become apparent.

White matter changes in dementia: does radiology matter?

White matter changes are frequently seen on MRI in elderly patients. The significance of these changes is still debated. The origin of white matter changes is heterogeneous but the majority are due to arteriosclerosis in brain vessels. The clinical consequence of the presence of white matter changes in relation to dementia is still unclear. Lately, however, many studies have found a relation between the presence and the degree of white matter changes and cognitive dysfunction. This is most obvious in vascular dementia, but has also been suggested to be of importance in Alzheimer's disease. In this review we discuss the background of these changes and the clinical consequences of them in relation to cognitive disorders.

Magnetic resonance imaging in dementia. A study of brain white matter changes

Non-specific white matter changes (WMC) in the brain are common findings in the elderly population. Although they are frequently seen in non-demented persons, WMC seem to be more common in demented patients. The significance of these changes, as well as their pathophysiological background, is incompletely understood. The aim of this thesis was to study different aspects of WMC using MR imaging (MRI) and to investigate the clinical significance of such changes in subjects with mild cognitive impairment or dementia. In study I post-mortem MRI of the brain was compared to corresponding neuropathology slices. WMC were quantified and found to be more extensive on neuropathology. The areas that appeared normal on MRI but not on histopathology represented only minor changes with increased distance between the myelinated fibres but with preserved axonal network and glial cell density. Study II evaluated the blood-brain barrier (BBB) integrity to investigate if an increased permeability could be shown in WMC. A contrast-enhanced MRI technique was used to detect small degrees of enhancement. No general increase in BBB could be detected in the WMC areas. In study III the relation between WMC and apolipoprotein E (APOE) genotype was explored in patients with Alzheimer's disease (AD). Results showed that AD patients, who were homozygous for the APOE epsilon 4 allele had more WMC than patients with other genotypes. This was most significant for changes in the deep white matter. Results also indicated that in AD patients carrying the epsilon 4 allele, WMC are not age-related phenomena, but might be related to the aetiology of the disease. Study IV aimed to investigate if WMC in a specific brain region affect cognitive functions related to that area. Periventricular WMC in the left frontal lobe predicted a decrease in initial word fluency, a test though to reflect left frontal lobe functioning. This indicates that WMC might have specific effects in different brain regions. In study V we evaluated the prognostic significance of WMC in patients with memory impairment, regarding the rate of further global cognitive decline. There was no difference in outcome between patients having extensive WMC and a matched control group, during 2-4 years of follow up, and assessed by the "Mini-Mental State Examination". In conclusion, this work has shown and characterised pathological changes in the white matter not visible on conventional MRI. We have also shown that there is no major general increase in BBB permeability in areas of WMC. In addition, homozygosity with regard to the APOE epsilon 4 gene allele implies an increased extent of WMC in AD patients. In AD patients carrying this gene allele, WMC are not merely age-related phenomena, but might be related to the aetiology of the disease. We also claim that WMC in a specific location might impair cognitive functions that rely on those specific pathways. In contrast, WMC do not seem to have any prognostic value in predicting the rate of global cognitive decline in patients at a memory clinic.