Structural connectivity in Parkinson's disease

In the last decades a rapid evolution of structural advanced MRI techniques has occurred supporting the diagnosis of idiopathic Parkinson's disease, allowing us to further investigate the disease progression from nigral to extra-nigral degeneration and finally to detect pre-manifest Parkinson's disease. Diffusion-weighted imaging and diffusion tensor imaging represent advanced morphological approaches useful to detect changes in white matter integrity. These techniques, indeed, by measuring the translational displacement of water molecules in terms of fractional anisotropy and mean diffusivity, represent a powerful tool for the visualization of white matter changes, offering a unique window on brain structural connectivity. Microstructural changes can either be extracted locally in predefined regions using a region of interest analysis and tractography or, alternatively, globally into the brain using a voxel-based analysis or tract-based spatial statistics. The aim of this report was not only to summarize the distribution and nature of these alterations in Parkinson's disease but also to highlight the potential correlations between clinical, cognitive parameters and microstructural tissue loss.