Hyponatremia in Cancer Patients

Hyponatremia is the most frequent electrolyte disorder in hospitalized patients but also a well-known poor prognostic factor in cancer patients. The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is often misdiagnosed by oncologists because of difficulties in the interpretation of laboratory tests. The etiology of hyponatremia is heterogeneous, but the predominant cause is an imbalance between excessive presence of water and serum sodium deficiency. Ectopic production of arginine vasopressin develops most frequently in small cell lung cancer, but also occurs in other malignancies. Neurological impairment may range from subclinical to life-threatening symptoms depending on the rate of serum sodium deficiency. Accurate diagnosis is essential to establish the appropriate therapy. When hyponatremia is caused by SIADH, hypertonic saline infusion is indicated for acute presentations whereas fluid restriction is preferred in cases of an asymptomatic chronic evolution. Other options include vasopressin receptor antagonists (“vaptans”) targeted specifically to the correction of euvolemic hyponatremia. The aim of this brief report is to provide concise and specific information for the management of SIADH in clinical practice in oncology.