Metabolic counterparts of sodium accumulation in multiple sclerosis: A whole brain ²³ Na-MRI and fast ¹ H-MRSI study

Background: Increase of brain total sodium concentrations (TSC) is present in multiple sclerosis (MS), but its pathological involvement has not been assessed yet. Objective: To determine in vivo the metabolic counterpart of brain sodium accumulation. Materials/methods: Whole brain ²³ Na-MR imaging and 3D- ¹ H-EPSI data were collected in 21 relapsing-remitting multiple sclerosis (RRMS) patients and 20 volunteers. Metabolites and sodium levels were extracted from several regions of grey matter (GM), normal-appearing white matter (NAWM) and white matter (WM) T ₂ lesions. Metabolic and ionic levels expressed as Z-scores have been averaged over the different compartments and used to explain sodium accumulations through stepwise regression models. Results: MS patients showed significant ²³ Na accumulations with lower choline and glutamate–glutamine (Glx) levels in GM; ²³ Na accumulations with lower N-acetyl aspartate (NAA), Glx levels and higher Myo-Inositol (m-Ins) in NAWM; and higher ²³ Na, m-Ins levels with lower NAA in WM T ₂ lesions. Regression models showed associations of TSC increase with reduced NAA in GM, NAWM and T ₂ lesions, as well as higher total-creatine, and smaller decrease of m-Ins in T ₂ lesions. GM Glx levels were associated with clinical scores. Conclusion: Increase of TSC in RRMS is mainly related to neuronal mitochondrial dysfunction while dysfunction of neuro-glial interactions within GM is linked to clinical scores.