Diffusely appearing white matter in multiple sclerosis: Insights from sodium (²³Na) MRI

Area of Science:

• Neuroimaging
• Biomarkers
• Multiple Sclerosis Pathophysiology

Background:

• Multiple Sclerosis (MS) is characterized by white matter lesions visible on MRI.
• Diffusely abnormal white matter (DAWM) represents ill-defined areas of intermediate signal intensity in MS.
• Quantitative assessment of DAWM using advanced MRI techniques remains underexplored.

Purpose of the Study:

• To detect and quantify tissue abnormalities in DAWM using sodium (23Na) MRI.
• To compare DAWM abnormalities with focal MS lesions and normal appearing white matter (NAWM).

Main Methods:

• Sodium (23Na) and conventional MRI were performed on 25 MS patients with DAWM (DAWM+), 25 MS patients without DAWM (DAWM-), and 10 healthy controls (HC).
• Mean total sodium concentrations (TSC) were quantified in DAWM, NAWM, normal appearing grey matter (NAGM), and focal MS lesions.

Main Results:

• TSC was elevated in NAGM and NAWM of MS patients compared to HC.
• DAWM exhibited sodium concentrations similar to NAWM.
• Focal MS lesions (T1 hypointense and T1 isointense) showed significantly higher TSC than DAWM.

Conclusions:

• Sodium (23Na) MRI is a sensitive technique for detecting subtle tissue abnormalities in MS.
• DAWM in MS demonstrates increased sodium levels comparable to NAWM.
• These findings suggest DAWM represents pathological changes less severe than focal lesions.