Background: Neuroaxonal loss is a major substrate of irreversible disability in multiple sclerosis, however, its cause is not understood. In multiple sclerosis there may be intracellular sodium accumulation due to neuroaxonal metabolic dysfunction, and increased extracellular sodium due to expansion of the extracellular space secondary to neuroaxonal loss. Sodium magnetic resonance imaging measures total sodium concentration in the brain, and could investigate this neuroaxonal dysfunction and loss in vivo. Sodium magnetic resonance imaging has been examined in small cohorts with relapsing-remitting multiple sclerosis, but has not been investigated in patients with a progressive course and high levels of disability.
Brain sodium is abnormal in MSers. #MSBlog #MSResearch
“This is work done by our UCL partners (UCLP) at UCL and describes a new MRI technique that can quantify sodium. MSers have increased brain sodium content and it appears to correlates with disability. Exactly what this means is subject to debate and it may suggest a new therapeutic target. We are very active in this field and testing various sodium channel blockers as neuroprotective agents in MS. Our optic neuritis and PROXIMUS study are testing two established sodium channel blockers in MS; i.e. phenytoin and oxcarbazepine. We plan to include sodium imaging in the PROXIMUS study. We will get an answer on whether or not we can modify this process with oxcarbazepine.”
Methods: They performed sodium magnetic resonance imaging in 27 healthy control subjects, 27 RRMSer, 23 with SPMSers and 20 with PPMSer. Cortical sodium concentrations were significantly higher in all subgroups of multiple sclerosis compared with controls, and deep grey and normal appearing white matter sodium concentrations were higher in primary and secondary-progressive multiple sclerosis.
Results: Sodium concentrations were higher in secondary-progressive compared with relapsing-remitting multiple sclerosis in cortical grey matter (41.3 ± 4.2 mM versus 38.5 ± 2.8 mM, P = 0.008), normal appearing white matter (36.1 ± 3.5 mM versus 33.6 ± 2.5 mM, P = 0.018) and deep grey matter (38.1 ± 3.1 mM versus 35.7 ± 2.4 mM, P = 0.02). Higher sodium concentrations were seen in T1 isointense (44.6 ± 7.2 mM) and T1 hypointense lesions (46.8 ± 8.3 mM) compared with normal appearing white matter (34.9 ± 3.3 mM, P < 0.001 for both comparisons). Higher sodium concentration was observed in T1 hypointense lesions in secondary-progressive (49.0 ± 7.0 mM) and primary-progressive (49.3 ± 8.0 mM) compared with relapsing-remitting multiple sclerosis (43.0 ± 8.5 mM, P = 0.029 for both comparisons). Independent association was seen of deep grey matter sodium concentration with expanded disability status score (coefficient = 0.24, P = 0.003) and timed 25 ft walk speed (coefficient = -0.24, P = 0.01), and of T1 lesion sodium concentration with the z-scores of the nine hole peg test (coefficient = -0.12, P < 0.001) and paced auditory serial addition test (coefficient = -0.081, P < 0.001).
Conclusions: Sodium concentration is increased within lesions, normal appearing white matter and cortical and deep grey matter in multiple sclerosis, with higher concentrations seen in secondary-progressive multiple sclerosis and in patients with greater disability. Increased total sodium concentration is likely to reflect neuroaxonal pathophysiology leading to clinical progression and increased disability.