Lower limb disability in multiple sclerosis (MS) is likely related to axonal damage in the corticospinal tract (CST), the main motor pathway. This study aimed to compare the degree of CST degeneration to clinical motor disability using high field (7T) diffusion weighted MRI and subsequent analyses methods like tractography and fixel-based analysis. Eleven minimally impaired relapsing-remitting MS patients (1m/10f, 42±12.4yrs) were tested. Results show loss of fiber density (FD) in the subcortical white matter of the CST was associated with increased pyramidal dysfunction (puncorrected<0.05). FD could provide a useful marker of disease progression leading to loss of mobility.