31-24 – White matter microstructure changes across motor phenotype in newly diagnosed Parkinson’s disease

An increasing body of research suggests abnormal changes in the white matter pathways are common in newly diagnosed people with Parkinson’s disease (PwP) and could be responsible for inter-patient differences in clinical symptomatology. People with newly diagnosed tremor-dominant Parkinson’s disease (TD-PD) exhibit increased fractional anisotropy (FA), conversely the PD motor phenotype postural instability gait difficulty (PIGD-PD) shows decreased FA early in the disease course. We utilised a de novo TD-PD and PIGD-PD cohort and novel tract segmentation methodology, TractSeg, to investigate along the tract abnormalities associated with the PD motor phenotypes.

Data was collected from the PPMI for PwP and healthy controls (HC). We collected baseline, T1, T2 and DWI images to analyse white matter FA alterations. Demographics and UPDRS were collected to match for age, sex and motor severity. The UPDRS was used to assess TD-PD and PIGD-PD subtypes and severity of motor symptoms. The extracted images were pre-processed using FSL and MRtrix. TractSeg segments tracts into field of fiber orientation distribution (fODF) peaks and produces 50 bundle–specific FA tractograms including 98 regions for each tract.

137 PwP and 63 controls were included in the analysis. From the PwP group 104 were defined as TD-PD and 33 were defined as PIGD-PD. We used the stats model built in TractSeg to assess group differences. 18 tracts in the TD-PD showed increases in FA compared to the HC and one tract with decreased FA. The PIGD-PD group showed 3 tracts with increased FA and one tract with decreased FA compared to HC. These results did not survive multiple comparisons between the tracts.

Multiple tracts exhibited areas of increased FA in TD-PD and PIGD-PD – more specifically several tracts related to motor control and initiation were indicated. Increased FA in TD-PD has previously been reported, implying neural reorganisation to compensate for PD pathology in the early stages.