Metabolic counterparts of sodium accumulation in multiple sclerosis: A whole brain Na-MRI and fast 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 Na-MR imaging and 3D-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 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 Na accumulations with lower choline and glutamate-glutamine (Glx) levels in GM; Na accumulations with lower N-acetyl aspartate (NAA), Glx levels and higher Myo-Inositol (m-Ins) in NAWM; and higher Na, m-Ins levels with lower NAA in WM T lesions. Regression models showed associations of TSC increase with reduced NAA in GM, NAWM and T lesions, as well as higher total-creatine, and smaller decrease of m-Ins in T 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.