Objective: This study aimed to extend current knowledge on symptomatic heterogeneity in Parkinson’s disease (PD) by investigating structural alterations underpinning FC.

Background: The postural instability and gait disorder (PIGD) subtype has specific alterations in functional connectivity when compared to the tremor dominant (TD) subtype.

Methods: 68 PD patients classified as PIGD (n=41) or TD (n=19) and 19 healthy age-matched controls underwent Magnetic Resonance Imaging (MRI). Diffusion weighted images were used for probabilistic tractography between regions that previously showed altered FC. In addition, tract-based spatial statistics (TBSS) were used to assess fractional anisotropy (FA) and mean diffusivity (MD) at the whole-brain level. Anatomical images were used to determine shape and volume of the putamen, caudate and pallidum.

Results: TD showed increased MD compared to PIGD and controls in the tracts connecting the right inferior parietal lobule with the right premotor and primary motor cortex, which previously showed altered functional connectivity. In addition, PD subgroups had increased MD compared to controls in tracts connecting the left caudate with the bilateral ventral putamen. TBSS revealed widespread FA reductions in PIGD compared to controls involving the superior longitudinal fasciculi and corpus callosum. No such differences were found in TD. We also found grey matter atrophy in the rostrodorsal head of the caudate in PIGD compared to controls and a similar trend in PIGD compared to TD.

Conclusions: Functional connectivity alterations in PD subtypes are partly underlain by microstructural characteristics in white matter tracts. Caudate shape alterations further implicate the striatum in PIGD pathophysiology.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-subtypes-in-parkinsons-disease-are-distinguished-by-alterations-in-morphology-and-white-matter-integrity/