Objective: The aim of this study was to detect disrupted structural connectivity in Parkinson’s disease (PD) patients classified according to their cognitive status, with and without mild cognitive impairment (MCI), and healthy controls (HC), and to find correlations between the disrupted connections and the neuropsychological performance.

Background: Threshold‐free network‐based statistics (TFNBS) has been demonstrated to be a useful technique to study structural connectivity in neurodegenerative disorders [1] and although PD is known to progress with structural dysfunction; to the best of our knowledge, there are no previous studies using TFNBS to study structural connectivity in PD with and without MCI.

Method: Sixty-one PD patients of which 26 had MCI, and 51 HC were evaluated using diffusion-weighted MRI on a 3T scanner. Structural connectivity, represented by number of streamlines (NOS), was derived from probabilistic tractography using FSL Bedpostx and Probtrackx tools [2]. Then, TFNBS [3] was used to evaluate differences in structural connectivity between groups. The neuropsychological battery recommended by the Movement Disorder Society task force [4] was used to evaluate the main cognitive domains: attention/working memory; executive function, memory, and the visuospatial/visuoperceptual domain. Matlab was used to perform correlations between NOS and the test scores, both converted to Z-scores. Correlations were FDR corrected.

Results: There were no differences in age or years of education, but there were in gender (χ²=9.96, p=0.007). PD patients showed reduced NOS when compared with HC in 117 ROI pairs (p<0.05, FWE-corrected). These connections were cortico-cortical or subcortico-cortical and intra- and inter-hemispheric. When PD with and without MCI were considered separately, both had reduced connectivity, but only PD-MCI patients had significant correlations with the neuropsychological performance. Concretely, Stroop color and Stroop interference correlated with cortico-cortical as well as cortico-subcortical connections.

Conclusion: PD present widespread reduced structural connectivity when compared with HC using a probabilistic connectivity approach and TFNBS. Qualitatively, PD-MCI present a higher number of impaired connections than PD without MCI. Moreover, in PD-MCI patients, several altered connections correlated with measures of Stroop test performance that measure the speed of mental processing.

References: 1. Abos, A., Segura, B., Baggio, H. C., Campabadal, A., Uribe, C., Garrido, A., Camara, A., Muñoz, E., Valldeoriola, F., Marti, M. J., Junque, C., & Compta, Y. Disrupted structural connectivity of fronto-deep gray matter pathways in progressive supranuclear palsy. NeuroImage Clinical 2019; 23. 2.Behrens, T.E.J., Berg, H.J., Jbabdi, S., Rushworth, M.F.S., Woolrich, M.W. Probabilistic diffusion tractography with multiple fibre orientations : what can we in? Neuroimage 2007; 34:144-155. 3.Baggio, H.C., Abos, A., Segura, B., Campabadal, A., Garcia-Diaz, A., Uribe, C., Compta, Y., Marti, M.J., Valldeoriola, F., Junque, C. Statistical inference in brain graphs using threshold-free network-based statistics. Hum. Brain Mapp 2018; 39. 4.Litvan I, Aarsland D, Adler CH, et al. MDS Task Force on mild cognitive impairment in Parkinson’s disease: critical review of PD- MCI. Mov Disord 2011; 26:1814-1824.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impaired-structural-connectivity-in-parkinsons-disease-and-its-neuropsychological-correlates/