Motor-related circuit dysfunction in MSA-P: Usefulness of combined whole-brain imaging analysis

The aim of this study was to evaluate in vivo changes in the brain's macro- and microstructure (notably in the motor system) in the parkinsonian variant of multiple system atrophy (MSA-P) and in Parkinson's disease (PD) and to characterize the cerebral anatomical differences between the two conditions. We used a combination of voxel-based morphometry (VBM) and whole-brain, voxel-based diffusion tensor imaging analysis (VB-DTI). Forty-seven right-handed subjects (14 MSA-P patients, 19 PD patients, and 14 controls) were evaluated using VBM and VB-DTI in an analysis of covariance (ANCOVA) with a significance threshold set to P < 0.005. In MSA-P patients, VBM analysis revealed a lower density of grey matter (GM) in a motor-related circuit (especially in the left primary motor cortex, PMC), relative to PD patients, and in the left supplementary motor area (SMA), relative to controls). Diffusion tensor imaging analysis revealed lower fractional anisotropy (FA) values in the left PMC and the right cerebellum in MSA-P patients, compared with controls. Using a volumetric diffusion technique, our study revealed selective tissue degeneration in motor circuits, regardless of the volume loss detected in VBM and in agreement with pathology reports and clinical motor characteristics. Our findings suggest that MSA-P is characterized by both macro- and microstructural changes in the sensorimotor circuit.