Olfactory Impairment in Parkinson’s Disease Studied with Diffusion Tensor and Magnetization Transfer Imaging

Abstract

Background: Olfactory impairment is an early manifestation of Parkinson’s disease (PD). Diffusion Tensor Imaging (DTI) and Magnetization Transfer (MT) are two imaging techniques that allow noninvasive detection of microstructural changes in the cerebral white matter.Objective: To assess white matter alterations associated with olfactory impairment in PD, using a binary imaging approach with DTI and MT.Methods: 22 PD patients and 13 healthy controls were examined with DTI, MT and an odor discrimination test. DTI data were first analyzed with tract-based spatial statistics (TBSS) in order to detect differences in fractional anisotropy, mean, radial and axial diffusivity between PD patients and controls. Voxelwise randomized permutation was employed for the MT analysis, after spatial and intensity normalization. Additionally, ROI analysis was performed on both the DTI and MT data, focused on the white matter adjacent to olfactory brain regions.Results: Whole brain voxelwise analysis revealed decreased axial diffusivity in the left uncinate fasciculus and the white matter adjacent to the left olfactory sulcus of PD patients. ROI analysis demonstrated decreased axial diffusivity in the right orbitofrontal cortex, as well as decreased mean diffusivity and axial diffusivity in the white matter of the left entorhinal cortex of PD patients. There were no significant differences regarding fractional anisotropy, radial diffusivity or MT between patients and controls.Conclusions: ROI analysis of DTI could detect microstructural changes in the white matter adjacent to olfactory areas in PD patients, whereas MT imaging could not.

White matter alterations in Parkinson’s disease with normal cognition precede grey matter atrophy

“…Similarly to some of previous PD studies [ 54 , 58 , 59 ], but contradictory to the others [ 60 , 61 ], we detected an increase in AD in PD-NCI compared to HC. AD is considered a measure of axonal consistency with higher values potentially indicating an increase of axonal co-linearity, however axonal loss in co-occurrence of inflammation [ 62 ] may provide additional explanation to elevated AD in the PD population.…”

Diffusion Tensor Imaging in Parkinson's Disease and Parkinsonian Syndrome: A Systematic Review

“…Braak et al (3) suggested that Lewy bodies are mainly confined to the medulla oblongata/pontine tegmentum and olfactory bulb/anterior olfactory nucleus in the earliest stages of PD. Using voxel-based analysis, two studies (90,148) found PD is associated with abnormal diffusivity in white matter tracts adjacent to the olfactory sulcus. Although tractography of the olfactory tract is practically difficult in this area, using ROI drawing, some studies (92,119,122) reported low FA of the olfactory tract in PD.…”

Structural white matter alterations as compensatory mechanisms in Parkinson's disease: A systematic review of diffusion tensor imaging studies

“…Several studies have shown that various parts of CC, including body and splenium of CC and cingulum, possess higher microstructural organization (indicated by the higher FA and lower diffusion) in patients with PD compared to HCs (Georgiopoulos et al, 2017; Taylor et al, 2018; Wen et al, 2016, 2018). Connectometry also demonstrated a higher WM density of CC in both HY1 PD and HY2 PD patients compared to HCs (Wen et al, 2016).…”