Subcortical grey matter changes associated with motor symptoms evaluated by the Unified Parkinson’s disease Rating Scale (part III): A longitudinal study in Parkinson’s disease

•Decreased grey matter volume over time suggests a subcortical alteration in PD.•Decreased volume in the thalamus may be related to the decline in motor skills.•Increased volume in the pallidum may contribute to motor impairment.•Structural changes in line with the model of basal ganglia-thalamocortical circuits.•VBM and volumetry might capture complementary aspects of structural changes in PD.