[Hyponatremia in clinical practice]

Hyponatremia is the most frequent electrolyte disorder in hospitalized patients and it is associated with unfavorable clinical outcomes as well as increased hospital costs. Its clinical presentation may be highly variable, ranging from asymptomaticity to neurologic emergencies with seizures or coma as signs of rapidly worsening cerebral edema. In these cases, prompt treatment is mandatory to avoid the patients death. On the other hand, in the case of gradual development of hyponatremia, it is imperative that its correction be also appropriately slow in order to avoid another neurological catastrophe, namely the osmotic demyelination syndrome. Whilst recent international guidelines and expert consensus agree on the approach to the treatment of acute severe and symptomatic hyponatremia, the recommendations on pharmacological therapy in chronic hyponatremia diverge, particularly as to the potential use of vasopressin antagonists. This review is aimed at summarizing essential aspects of epidemiology, pathophysiology and the diagnostic process of hyponatremia, to set the ground for a practical as well as evidence-based approach to treatment. As a guide through the discussion of the available evidence, a clinical case is presented in which the patients history and laboratory data are crucial for identifying the etiology of hyponatremia. The severe neurological signs at presentation justify an emergency treatment with hypertonic saline, as indicated. Subsequently, as the neurological emergency subsides, we discuss the need to revert the trend towards hypercorrection by an apparently counterintuitive approach, based in fact on sound pathophysiological grounds, with continuous infusion of hypotonic solutions and administration of desmopressin.