Hyponatremia in Depression: A Review

Hyponatremia is a prevalent and potentially dangerous medical comorbidity in psychiatric patients which may be clinically characterized as serum sodium concentration less than 136 mEq/L. Hypernatremia is almost always due to a deficiency of water intake, as a result of either a thirst defect or inaccessibility of water. Psychiatric disorders in general are associated with a higher risk of hyponatremia. The increased risk is primarily attributable to the elevated frequency of primary polydipsia and the prescribing of medications which impair water excretion. Hyonatremia represents an abnormal ratio of total body sodium to water.When hyponatremia occurs, the resulting decrease in plasma osmolality with the exception of the rare cases of non-hypoosmotic hyponatremia causes water movement into the brain in response to the osmotic gradient, thus causing cerebral oedema. Hyponatremia typically develops in the context of an underlying disruption of free water elimination, usually as a result of arginine vasopressin (AVP) release or renal failure, also known as antidiuretic hormone, is a peptide hormone produced by the hypothalamus and transported via axons to the posterior pituitary, from which it is released. The association between antidepressants and hyponatremia has been studied extensively in recent years. Evidence that impaired water excretion predates antipsychotic medications or antipsychotics do not generally increase AVP levels and indeed normalize elevated levels in some with acute psychosis or dose reduction does not improve hyponatremia or lower, not higher, doses are more likely to be associated with hyponatremia. We prepared this review to strengthen the correlation between hyponatremia and depression.