Mitochondrial injury and impaired metabolic capacity are hypothesized to drive neurodegeneration in multiple sclerosis (MS). Here, we investigate a novel putative marker of tissue metabolic activity, trans-capillary water flux, derived from dynamic contrast enhanced MRI. In this study we compared 23 subjects with progressive MS to 19 healthy controls. We find significantly reduced measures on capillary water flux in MS thalami compared to controls. Implications for use of this new biomarker are discussed.