Hyponatremia in cancer patients: Much more than a common electrolytic disorder

Hyponatremia is a common electrolytic disorder, frequently encountered in patients with malignant tumors. In oncology, most cases of hyponatremia are caused by the syndrome of inappropriate secretion of antidiuretic hormone (SIADH).
This syndrome occurs most frequently in small cell lung cancer. Most cases of hyponatremia develop in the presence of water excess relative to sodium, due to inability of the kidneys to excrete water. A small percentage of cases present hyponatremia secondary to excessive water intake. SIADH is a diagnosis of exclusion. The patients are clinically euvolemic, without edema or ascites.
The presence of hyponatremia in patients with malignant disease is associated with decreased survival, increased duration of hospitalization and higher intrahospital death rates. The treatment of hyponatremia depends on the severity of hyponatremia, the clinical manifestations and the extracellular volume status of the patient. The initial management of asymptomatic patients with euvolemic or hypervolemic hyponatremia consists in fluid restriction, in order to obtain a negative water balance.
The correction of hyponatremia in symptomatic patients with SIADH is obtained with hypertonic saline solution. A new class of drugs for the treatment of hyponatremia is represented by vasopressin antagonists.