Supplementary motor area microstructure as measured by diffusion imaging defines the extent of gait impairment in Parkinson’s disease

Gait disorders are therapeutically challenging symptoms in Parkinson’s disease. However, the pathophysiological mechanisms and the interaction between cerebral structure and clinical burden are not yet fully understood. Objectives: Given that cortical microstructure is a crucial determinant of symptom burden in neurodegenerative diseases, we hypothesized that diffusion-imaging-based microstructural markers in the supplementary motor area, one cortical key hub in the gait network, are associated with gait performance. Methods: In this retrospective study, 29 patients (mean age 64.1 ± 6.9 years, 11 (37.9%) female, mean disease duration 10.9 ± 4.5 years) were included. Diffusion-tensor imaging measures and cortical thickness (fractional anisotropy, radial and axial diffusivity) in the supplementary motor area as defined by the Human Motor Area Template were correlated with quantitative gait performance parameters. Results: Lower anisotropy in the right supplementary motor cortex was significantly associated with better performance across various bilateral gait parameters during walking at natural speed, at maximal velocity and particularly during dual-tasking. There were no significant associations between cortical thickness and gait performance. Conclusions: Given the inverse relationship between anisotropy and cortical tissue complexity, the observed lower anisotropy in the right supplementary motor area of patients with better gait performance supports the assumption of the modulatory role of this cortical area in gait control suggesting a potential therapeutic target e.g. stimulation, in Parkinson’s disease patients with gait disorders.