Impact of hyponatremia on nerve conduction and muscle strength

BackgroundHyponatremia is associated with unstable gait and propensity to falls. The potential contribution of peripheral nervous system dysfunction induced by hyponatremia has not yet been addressed by prospective studies. DesignIn the first part of this prospective study, we performed two tests evaluating muscle strength (grip test and quadriceps isometric contraction test) together with a timed up and go (TUG) test in 11 patients with chronic mild-to-moderate hyponatremia before and after the normalization of natremia. In the second part, we measured nerve conduction velocities and F-wave latencies in nine patients with profound hyponatremia (< 125 mmol/L) before and after the normalization of natremia. ResultsNo significant change in muscle strength was observed when natremia was corrected from 1277 25 to 1361 +/- 18 mmol/L, contrary to a significant improvement in TUG from 149 +/- 51 to 125 +/- 47 s (P = 0006). Nerve conduction velocities and F-wave latencies showed significant improvement in most of the studied nerves when natremia was corrected from 1219 +/- 24 to 1355 +/- 34 mmol/L (e.g. mean increase of 143% for motor nerve conduction and mean decrease of 216% for F-wave latency of left peroneal nerve). ConclusionWhereas chronic mild-to-moderate hyponatremia has no impact on muscle strength, we demonstrate for the first time an impact of profound hyponatremia on nerve conduction studies. Further studies are needed to ascertain the contribution of these latter results on gait disturbances, propensity to falls and attention deficits associated with hyponatremia.