Objective: To assess diffusion tensor imaging differences between PD patients and healthy controls in 8 corticospinal tract segments.

Background: Parkinson’s disease (PD), despite having motor and non-motor symptoms, is mostly known by its motor features. The corticospinal tract is the major motor tract and is related to a variety of movements, such as gait, writing, typing, buttoning, which are all impaired in PD.

Method: We included 40 PD patients (mean age 60 years) and 129 healthy controls (mean age 58 years). Demographics are described in table 1. 
DTI microstructural parameters of the cortical-spinal tract (CST) were obtained using the software ExploreDTI. The DTI images were corrected for signal drift, Gibbs’ rings, susceptibility artifact, Eddy currents, and movement and then registered to a subject T1 weighted image. We used a semi-automatic methodology for fiber tracking based on strategies drawn on a reference template. The tracts were uniformly resampled and divided into 8 segments [Figure1]. We ran a repeated measures analysis of variance with mixed designs, including the effect of segments (within-subjects), an effect of group (between-subjects) and a segment* group interaction. Significant interactions were evaluated using analysis of simple effects. We report Huynh-Feldt corrected F tests to account for deviations of sphericity assumption. Multiple comparisons were corrected using the false discovery rate (group effect) and Sidak tests (segments).

Results: We found a significant difference between PD and controls F_1,161 = 48.4, p<0.001, a significant difference within segments F_3,521 = 159.6, p<0.001 and significant group*segment interaction F_3,521 = 18.1, p<0.001 (Figure 1). Overall, PD patients showed higher FA than controls in all (p<0.02) but the 4^th segment (p=0.65).

Conclusion: The fractional anisotropy is higher in PD patients when compared to controls. Its values are also different among segments, and the same pattern is seen in controls.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/tractography-of-the-corticospinal-tract-in-parkinsons-disease-how-does-diffusion-values-vary-along-tract-segments/