Neurological aspects of hyponatraemia

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Abstract
Summary: Hyponatraemia is a common biochemical finding, but clinical features due to it are infrequent. They are most likely to occur when the plasma sodium concentration has fallen quickly to below 120 mmol/litre. In a study of 73 hyponatraemic individuals, it was possible to identify four categories of patient, the clinical features becoming more severe as the sodium level fell. In 25 instances there were no effects (mean plasma sodium 118\u00b73 mmol/litre), in a further 25 cases there was confusion only (mean plasma sodium 117\u00b71 mmol/litre), in 13 there were focal neurological signs and in 10 there were convulsions (mean plasma sodium 110\u00b78 mmol/litre). In the group with convulsions there were six deaths, the four survivors all being young women. The 13 cases of \u2018focal\u2019 neurological signs included three instances each of hemiparesis and monoparesis, seven of extra-pyramidal disturbance and six of cerebellar ataxia. All these abnormalities resolved when the plasma sodium concentration rose to 125 mmol/litre. Active measures to raise the plasma sodium level are only needed when there have been convulsions and the aim should be to achieve a value no higher than 120 mmol/litre. In other cases, the only treatment required is to restrict fluid intake.