This interesting study from the UK looked at sodium MR imaging in 27 healthy controls, 27 people with relapsing-remitting MS (RRMS), 23 people with secondary progressive MS (SPMS) and 20 people with primary progressive MS (PPMS). They hypothesised that in MS, there may be intracellular sodium accumulation due to neuroaxonal metabolic dysfunction and increased extracellular sodium due to expansion of the extracellular space as a result of neuroaxonal loss.
They found that cortical sodium concentrations were significantly higher in all sub-groups of MS compared with controls. They also found that deep grey and normal appearing white matter sodium concentrations were higher in primary and secondary-progressive MS. Sodium concentrations were higher in secondary-progressive compared with RRMS in cortical grey matter, normal appearing white matter and deep grey matter. Higher sodium concentrations were seen in T1 isointense and T1 hypointense lesions compared with normal appearing white matter. Also, higher sodium concentrations were seen in T1 hypointense lesions in SPMS and PPMS compared to RRMS.
The researchers observed independent associations of deep grey matter sodium concentration with EDSS and timed 25-foot walk speed as well as T1 lesion sodium concentration with the z-scores of the nine hole peg test and paced auditory serial test (PASAT). They suggest that the increased sodium concentration is likely to reflect neuroaxonal pathophysiology leading to clinical progression and disability progression.
Authors: Paling D, Solanky BS
Source: Brain. 2013 Jul;136(Pt 7):2305-17. doi: 10.1093/brain/awt149.
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