Advanced magnetic resonance imaging (MRI) techniques provide a window into pathological processes in multiple sclerosis (MS). Nevertheless, to date only few studies have performed sodium MRI in MS.

We analysed total sodium concentration (TSC) in hyperacute, acute and chronic lesions in MS with ²³Na MRI.

²³Na MRI and ¹H MRI were performed in 65 MS patients and 10 healthy controls (HC). Mean TSC was quantified in all MS lesions with a diameter of >5 mm and in the normal appearing white and grey matter (NAWM, NAGM).

TSC in the NAWM and the NAGM of MS patients was significantly higher compared to HC (WM: 37.51 ± 2.65 mM versus 35.17 ± 3.40 mM; GM: 43.64 ± 2.75 mM versus 40.09 ± 4.64 mM). Acute and chronic MS lesions showed elevated TSC levels of different extent (contrast-enhancing lesions (49.07 ± 6.99 mM), T1 hypointense lesions (45.06 ± 6.26 mM) and remaining T1 isointense lesions (39.88 ± 5.54 mM)). However, non-enhancing hyperacute lesions with a reduced apparent diffusion coefficient showed a TSC comparable to the NAWM (37.22 ± 4.62 mM).

TSC is not only a sensitive marker of the severity of chronic tissue abnormalities in MS but is also highly sensitive to opening of the blood–brain barrier and vasogenic tissue oedema in contrast-enhancing lesions.