White matter tract integrity in aging and Alzheimer's disease

Abstract

The pattern of degenerative changes in the brain white matter (WM) in aging, mild cognitive impairment (MCI), and Alzheimer's disease (AD) has been under debate. Methods of image analysis are an important factor affecting the outcomes of various studies. Here we used diffusion tensor imaging (DTI) to obtain fractional anisotropy (FA) measures of the WM in healthy young (n = 8), healthy elderly (n = 22), MCI (n = 8), and AD patients (n = 16). We then applied "tract-based spatial statistics" (TBSS) to study the effects of aging, MCI, and AD on WM integrity. Our results show that changes in WM integrity (that is, decreases in FA) are different between healthy aging and AD: in healthy older subjects compared with healthy young subjects decreased FA was primarily observed in frontal, parietal, and subcortical areas whereas in AD, compared with healthy older subjects, decreased FA was only observed in the left anterior temporal lobe. This different pattern of decreased anatomical connectivity in normal aging and AD suggests that AD is not merely accelerated aging.

Age-related changes in human and non-human primate white matter: from myelination disturbances to cognitive decline

“…Mildly impaired AD subjects also showed small decrements in FA in the posterior callosum and subcortical WM compared with normal age-matched adults, which correlated with specific functional impairments (Kavcic et al 2008). A similar result showed that normal aged and mildly cognitively impaired (MCI) subjects differed from AD, in that the latter had a differential decrease of FA in the left anterior temporal lobe, consistent with disease progression (Damoiseaux et al 2009). Interestingly, lower FA was associated significantly with coincident AD and vascular brain injury (Back et al 2011).…”

In Vivo Structural Neuroanatomy of Corpus Callosum in Alzheimer's Disease and Mild Cognitive Impairment Using Different MRI Techniques: A Review

“…Furthermore, the findings of studies on more homogeneous patients, such as those with mild AD, are discrepant. For example, Xie et al [82] found a decrease of FA in the genu and left anterior body of the CC, whereas Ulkmar et al [83] found a decrease of FA in the genu and splenium of the CC; other studies [84][85][86][87] found no differences in the CC in patients with mild AD.…”

Individual Classification of Mild Cognitive Impairment Subtypes by Support Vector Machine Analysis of White Matter DTI

“…Most investigations included only 1 (not further specified) MCI group, [23][24][25] or only the sd-aMCI subtype, [26][27][28][29] or a mix of several subtypes, with the aim of discriminating stable versus progressive MCI. 30 Only 3 recent contributions compared DTI patterns in aMCI versus non-MCI.…”

“…First, a group-level analysis using TBSS, 22 an improved voxel-based technique with respect to spatial normalization, was performed to identify regions with altered white matter structure between groups. As discussed above, recent investigations implementing this technique in the domain of MCI 23,24,28 documented the presence of reduced FA primarily in white matter tracts with homogeneously oriented fibers (ie, genu or splenium of the corpus callosum, superior longitudinal fasciculus, cingulus) and, more rarely, in frontal, parietal, and temporal white matter. However, other studies led to negative data challenging this point of view.…”

“…Applying DTI analyses with voxelwise TBSS, 22 an increasing number of contributions described the damage of long interhemispheric and intrahemispheric white matter tracts with homogeneously oriented fibers (ie, genu or splenium of the corpus callosum, superior longitudinal fasciculus, cingulus) and, more rarely, in frontal, parietal, and temporal white matter in patients with MCI compared with healthy controls. [23][24][25][26][27][28][29][30][31] The biologic relevance of the description of MCI subtypes is still a challenging issue. In particular, it is unclear whether the neuropsychologic definition of these subtypes corresponds to distinct patterns of brain compromise.…”