Abstract
The structural connectivity within cortical areas and between cortical and subcortical structures was investigated in dementia with Lewy bodies (DLB) and Alzheimer’s disease (AD). We hypothesized that white matter (WM) tracts, which are linked to visual, attentional, and mnemonic functions, would be differentially and selectively affected in DLB as compared to AD and age-matched control subjects. Structural tensor imaging and diffusion tensor imaging (DTI) were performed on 14 DLB patients, 14 AD patients, and 15 controls. DTI metrics related to WM damage were assessed within tracts reconstructed by FreeSurfer’s TRActs Constrained by UnderLying Anatomy pipeline. Correlation analysis between WM and gray matter (GM) metrics was performed to assess whether the structural connectivity alteration in AD and DLB could be secondary to GM neuronal loss or a consequence of direct WM injury. Anterior thalamic radiation (ATR) and cingulum-cingulate gyrus were altered in DLB, whereas cingulum-angular bundle (CAB) was disrupted in AD. In DLB patients, secondary axonal degeneration within ATR was found in relation to microstructural damage within medio-dorsal thalamus, whereas axonal degeneration within CAB was related to precuneus thinning. WM alteration within the uncinate fasciculus was present in both groups of patients and was related to frontal and to temporal thinning in DLB and AD, respectively. We found structural connectivity alterations within fronto-thalamic and fronto-parietal (precuneus) network in DLB whereas, in contrast, disruption of structural connectivity of mnemonic pathways was present in AD. Furthermore, the high correlation between GM and WM metrics suggests that the structural connectivity alteration in DLB could be linked to GM neuronal loss rather than by direct WM injury. Thus, this finding supports the key role of cortical and subcortical atrophy in DLB.
Highlights
Because the axonal degeneration can be initiated either by the degeneration of the cell bodies associated with these axons, or by the direct white matter (WM) injury, we performed a correlation analysis between WM and gray matter (GM) metrics to assess whether possible structural connectivity alteration in Alzheimer’s disease (AD) and dementia with Lewy bodies (DLB) could be the consequence of GM neuronal loss
Within the AD group, no significant correlation was found between Diffusion Tensor Imaging (DTI) metrics in the right and left cingulum-cingulate gyrus (CCG) bundle and GM measure in the target regions; the increase of DA values within the right uncinate fasciculus was correlated to right STG thickness (t = −3.427, β = −0.703, p = 0.005)
We found specific pattern of WM alterations in DLB and AD
Summary
Dementia with Lewy bodies (DLB) is the second most common form of neurodegenerative dementia after Alzheimer’s disease (AD) (Vann Jones and O’Brien, 2014). Different approaches have been used to assess the structural connectivity in DLB patients They ranged from conventional analyses, which use region of interest (ROI) (Bozzali et al, 2005) or tract-specific method (Ota et al, 2009) to voxel-based approaches, which use statistical parametrical mapping analysis (Lee et al, 2010) or tract-based spatial statistics (Hattori et al, 2012; Watson et al, 2012). TRACULA has benefits in terms of: (1) overcoming the limitations related to manual interaction, facilitating the application of tractography to large studies; (2) measuring, for each patient, the DTI-derived metrics from each tract of interest; (3) overcoming coregistration issues linked to voxel-based approaches (Wassermann et al, 2011; Yendiki et al, 2011, 2013). Because the axonal degeneration can be initiated either by the degeneration of the cell bodies associated with these axons, or by the direct WM injury, we performed a correlation analysis between WM and gray matter (GM) metrics to assess whether possible structural connectivity alteration in AD and DLB could be the consequence of GM neuronal loss
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