Regional MRI Diffusion, White-Matter Hyperintensities, and Cognitive Function in Alzheimer's Disease and Vascular Dementia

Abstract

Background and PurposeAn increase in brain water diffusivity as measured using magnetic resonance imaging (MRI) has been recently reported in normal-appearing white matter (NAWM) in patients affected by cognitive impairment. However, it remains to be clarified if this reflects an overt neuronal tissue disruption that leads to degenerative or microvascular lesions. This question was addressed by comparing the regional MRI apparent diffusion coefficients (ADCs) of NAWM in patients affected by Alzheimer's disease (AD) or vascular dementia (VaD). The relationships of ADCs with the white-matter hyperintensity (WMH) burden, carotid atherosclerosis, and cognitive performance were also investigated.MethodsForty-nine AD and 31 VaD patients underwent brain MRI to assess the WMH volume and regional NAWM ADCs, neuropsychological evaluations, and carotid ultrasound to assess the plaque severity and intima-media thickness (IMT).ResultsRegional ADCs in NAWM did not differ between VaD and AD patients, while the WMH volume was greater in VaD than in AD patients. The ADC in the anterior corpus callosum was related to the WMH volume, while a greater carotid IMT was positively correlated with the temporal ADC and WMH volume. The memory performance was worse in patients with higher temporal ADCs. Constructional praxis scores were related to ADCs in the frontal, and occipital lobes, in the anterior and posterior corpus callosum as well as to the WMH volume. Abstract reasoning was related to frontal, parietal, and temporal ADCs.ConclusionsOur data show that higher regional ADCs in NAWM are associated with microcirculatory impairment, as depicted by the WMH volume. Moreover, regional ADCs in NAWM are differently associated with the neuropsychological performances in memory, constructional praxia, and abstract reasoning domains.

Magnetic resonance imaging in Alzheimer’s disease and mild cognitive impairment

“…For patients along the AD spectrum, WMHs correlate with hippocampal atrophy [28], in addition to neuropsychological impairment and psychiatric disturbances [29, 30]. Considering differential diagnoses, patients with vascular dementia (VaD) have higher volumes of WMHs than in AD [31]. Periventricular WMHs are predictive of progression from MCI to AD, with an increase of one point in WMH rating associated with a 59% increased risk of phenoconversion [32].…”

Effectiveness of diffusion tensor imaging in differentiating early-stage subcortical ischemic vascular disease, Alzheimer’s disease and normal ageing

“…Typical neuroimaging features of patients with SIVD include hyperintensities extending into periventricular and deep white matter on T2-weighted magnetic resonance imaging (MRI), and lacunes within the deep gray matter [12]. However, both periventricular and deep white matter hyperintensities have also been documented in patients with AD [13,14] and in normal elderly subjects [15,16], making it a challenge to differentiate between SIVD and AD in the early stage, and even more for normal ageing process.…”

In vivomicrostructural heterogeneity of white matter lesions in Alzheimer’s disease using tissue compositional analysis of diffusion MRI data

“…Previous diffusion MRI research has attempted to investigate microstructural changes within WMH, by investigating these lesions using diffusion tensor imaging (DTI). These studies have investigated white matter mostly in terms of tensor metrics such as fractional anisotropy and/or mean diffusivity, and assessed how they may be altered in, or associated with WMH Firbank et al, 2003;Taylor et al, 2007;Vernooij et al, 2008;Lee et al, 2009;Topakian et al, 2009;Altamura et al, 2016;Seiler et al, 2018). Studies commonly report white matter microstructure, as measured using these DTI-derived metrics, to be altered not only within WMH (Bastin et al, 2009;Maniega et al, 2015), but additionally altered within NAWM in patients with such lesions (Firbank et al, 2003;Vernooij et al, 2008;Maniega et al, 2015).…”