Abstract
This study aimed to discriminate between neuroinflammation and neuronal degeneration in the white matter (WM) and gray matter (GM) of patients with Parkinson’s disease (PD) using free-water (FW) imaging. Analysis using tract-based spatial statistics (TBSS) of 20 patients with PD and 20 healthy individuals revealed changes in FW imaging indices (i.e., reduced FW-corrected fractional anisotropy (FAT), increased FW-corrected mean, axial, and radial diffusivities (MDT, ADT, and RDT, respectively) and fractional volume of FW (FW) in somewhat more specific WM areas compared with the changes of DTI indices. The region-of-interest (ROI) analysis further supported these findings, whereby those with PD showed significantly lower FAT and higher MDT, ADT, and RDT (indices of neuronal degeneration) in anterior WM areas as well as higher FW (index of neuroinflammation) in posterior WM areas compared with the controls. Results of GM-based spatial statistics (GBSS) analysis revealed that patients with PD had significantly higher MDT, ADT, and FW than the controls, whereas ROI analysis showed significantly increased MDT and FW and a trend toward increased ADT in GM areas, corresponding to Braak stage IV. These findings support the hypothesis that neuroinflammation precedes neuronal degeneration in PD, whereas WM microstructural alterations precede changes in GM.
Highlights
Parkinson’s disease (PD) is characterized by widespread aggregation of α-synucleinimmunoreactive inclusions in the form of Lewy pathology [1]
While changes in the doi:10.3390/cells8080839 www.mdpi.com/journal/cellsDiffusion tensor imaging (DTI) indices were observed across broad areas, changes in the free water (FW) imaging indices were observed in relatively limited areas
The increased MDT and ADT were predominantly observed in the anterior portion, whereas the increased FW was observed in the posterior white matter (WM)
Summary
Parkinson’s disease (PD) is characterized by widespread aggregation of α-synucleinimmunoreactive inclusions in the form of Lewy pathology [1]. DTI indices such as fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) characterize the orientation and distribution of the random movements of water molecules, diffusion magnitude, diffusional directionality perpendicular to the axon, and diffusional directionality along the axon, respectively [4]. Despite their sensitivity, DTI indices are not tissue specific [5]. A decrease in FA accompanied by increased MD may be attributed to neuronal degeneration and/or neuroinflammation [13]. The use of these indices might not be useful in differentiating between these pathologies
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