Sodium buildup in the brain correlates with MS disability

Images in 33-year-old man with early RR MS. Examples of substantial sodium accumulation in two macroscopic T2 lesions with two different signal intensity patterns at T1-weighted imaging: one lesion was hypointense (solid arrows) and one was isointense (dashed arrows) to normal-appearing WM on T1- weighted image. Source: Radiology (Zaaraoui et al)

A buildup of sodium in the brain detected by MRI may be a biomarker for the degeneration of nerve cells that occurs in patients with multiple sclerosis (MS), according to a study published online in Radiology.

Several key findings emerged from the study. The researchers found that patients with early-stage MS showed sodium accumulation in specific brain regions, while patients with more advanced disease showed sodium accumulation throughout the whole brain, including in normal-appearing areas. Sodium buildup in motor areas of the brain correlated directly to the degree of disability seen in the advanced-stage patients.

“A major challenge with multiple sclerosis is providing patients with a prognosis of disease progression,” Patrick Cozzone, PhD, director emeritus of the Center for Magnetic Resonance in Biology and Medicine, in Marseille, France, said in a release. “It’s very hard to predict the course of the disease.”

Experimental studies have suggested sodium accumulation may play a part in the development of neuronal injury that is the hallmark of MS. Thus, Cozzone and colleagues used 3T sodium MRI to study relapsing-remitting multiple sclerosis (RRMS).

The researchers conducted sodium MRI on 26 MS patients—14 with early-stage RRMS (less than five years in duration) and 12 with advanced disease (longer than five years)—as well as 15 age- and sex-matched control participants.

Cozzone and colleagues completed quantitative assessments of total sodium concentration (TSC) levels within MS lesions, white matter and gray matter.

In the early-stage RRMS patients, sodium MRI revealed abnormally high concentrations of sodium in specific brain regions, including the brainstem, cerebellum and temporal pole. “The early preferential susceptibility of these regions may be related to their high degree of connectivity, which increases their vulnerability to distant axonal injury.” In the advanced-stage RRMS patients, abnormally high sodium accumulation was widespread throughout the whole brain, including normal-appearing brain tissue.

Specifically, TSC values in normal-appearing white matter among participants with advanced MS were significantly higher than in control subjects. In the gray matter compartment, advanced patients also had significantly higher TSC values than those with early MS, which may reflect neuronal loss and neuronal dysfunction, according to the researchers. These values also were higher relative to control subjects for patients with advanced disease, but not those with early disease.

Because current treatments for MS are only able to slow the progress of the disease, the use of sodium accumulation as a biomarker of neuron degeneration may assist pharmaceutical companies in developing and assessing potential treatments. The method also may help monitor the occurrence of tissue injury and disability, according to Cozzone et al.

“Indeed, the results of this cross-sectional study must be confirmed in a larger group of patients and longitudinal follow-up studies are needed to better depict and understand the patterns of brain sodium accumulation and their clinical impact during the course of MS,” wrote Cozzone and colleagues.