Reversing hyponatremia may enhance cognition but reduce brain volume

A recent study has shown that among individuals with chronic hyponatremia, its correction leads to improved cognitive function as well as decreased brain volume and neuronal activity.

The study included 26 participants with presumed chronic hyponatremia without signs of hypo- or hypervolemia. Those with sodium levels <125 mmol/L were identified as having hyponatremia, with resolution defined as sodium levels >130 mmol/L after treatment.

Researchers performed standardized neuropsychological testing (Mini-Mental-State examination [MMSE], DemTect, Trail-Making Test [TMT] A/B, Beck’s Depression Inventory, Timed Up and Go) and resting-state magnetic resonance imaging (MRI) prior to and following treatment of hyponatremia to evaluate volumes of total brain, white and grey matter, as well as neuronal activity and its synchronization. Complete data were available for 21 patients.

In the cohort, mean sodium concentration was 118.4 mmol/L before treatment and 135.5 mmol/L after treatment. Treatment led to significant improvements in most measures of cognition.

Data from MRI studies, however, showed a decrease in brain tissue volumes, neuronal activity, and synchronization across all grey matter after normalization of sodium levels. These effects were particularly prominent in the hippocampus.

During hyponatremia, synchronization of neuronal activity showed a negative correlation with sodium levels (r=–0.836) and cognitive function (MMSE: r=–0.523; DemTect: r=–0.744; TMT-A: r=0.692).

The study was limited by the small sample size and insufficient quality of several MRI scans due to motion artifact.