[Hyponatremia: Differential Diagnosis and Treatment]

Hyponatremia is the most common electrolyte abnormality seen in hospitalized patients, with up to 30 % having a plasma sodium concentration below 135 mmol/l. It is now clear that the clinical problem extends beyond the neurological symptoms, which can be explained by intracerebral osmotic fluid shifts and brain edema. Instead, chronic hyponatremia is associated with impaired gait stability and an increased risk of bone fragility fractures. Moreover, hyponatremia has been demonstrated to be an indicator of poor prognosis in a variety of conditions.Hyponatremia can be a life-threatening disorder due to increased intracranial pressure, thus requiring prompt and efficacious treatment. However, overly rapid correction may be complicated by osmotic demyelination syndrome with catastrophic clinical sequelae, i. e., spastic quadriparesis, or even coma or death.To avoid inappropriate treatment, the underlying pathophysiology in each case as well as the time course (acute vs. chronic) and the clinical and biochemical severity must be considered.The purpose of this review is to provide the reader with a systematic approach to the correct diagnosis and management of hyponatremia based on available European and international guidelines.