Objective: Evaluate the correlation between brain tractography changes in patients with Parkinson’s disease (PD) with and without mild cognitive impairment (MCI).

Background: Up to 40% of PD patients have MCI early in the disease and PD patients with MCI (PD-MCI) have a higher risk of developing dementia compared to those with normal cognition (PD-NC). Finding an early marker for MCI in PD would help in reducing the potential of developing dementia in the event that neuroprotective and neurorestorative therapy becomes available.

Methods: 39 non-demented patients with PD and 16 healthy volunteers (HV) underwent a neuropsychological assessment and analyses of DWI data. Regions of interest were drawn using ITKSnap. Fiber tract analyses were performed using FiberNavigator and we studied the white matter parameters between cortical and subcortical structures.

Results: Patients with PD and normal cognition (PD-NC) had increased tract count compared with HV between the caudate nucleus (CAU) and the ipsilateral primary motor area (M1), while PD-MCI patients had a decrease in tract count compared with both groups and it was statistically significant with PD-NC (p=0.04). Other parameters revealed increased radial diffusivity (RD) and mean diffusivity (MD) in PD-NC vs. HV and in PD-MCI vs. PD-NC and HV. Increased RD is thought to reflect de/dys-myelination while increased MD has been associated with diminished membrane density. Similar patterns were observed between CAU and ipsilateral dorsolateral prefrontal cortex, supplementary motor area (SMA) and premotor cortices. Additionally, tractography analyses between CAU and ipsilateral SMA showed a pattern of increased axial diffusivity (AD) in PD-NC vs. HV, and a decreased AD in PD-MCI vs. PD-NC. Decreased AD was suggested to reflect axonal injury while increased AD might reflect brain maturation or compensation.

Conclusions: Our data reveal a significant increase in tract counts in PD-NC compared to HV and a significant decrease of this parameter in PD-MCI patients. This effect might reflect a compensational effect in PD-NC patients, which allows them to preserve the normal cognitive function. These results might serve as a marker for identifying the availability of compensational resources and for earlier prediction of the evolution of cognitive decline in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mild-cognitive-impairment-is-linked-with-white-matter-degeneration-in-the-cortico-subcortical-tracts-in-patients-with-parkinsons-disease/