[Hyponatremia: differential diagnosis and therapy]

Hyponatremia is the most commonly occurring electrolyte disorder and is associated with increased morbidity and mortality—independent of the underlying disease. Despite its high prevalence, hyponatremia is often underestimated and inadequately addressed in clinical routine. Depending on disease stage and severity, the electrolyte disorder can present with a wide spectrum of neurological signs and symptoms, ranging from adynamia and gait disturbances, to syncope or coma. While the underlying causes of hyponatremia may be manifold, their identification is crucial to initiating adequate therapeutic measures for symptomatic and causal therapy. The syndrome of inappropriate antidiuretic hormone (ADH) secretion (SiADH) is the most common cause of hyponatremia, present in 1/3 of hyponatremic patients and usually a result of medication, neurological, respiratory or malignant disease. A differential diagnostic approach using a simple algorithm that includes clinical and laboratory parameters is essential for identifying the underlying cause of hyponatremia and administering goal-directed therapy. The development of vaptans has provided new options in the treatment of SiADH-associated hyponatremia.