[Syndrome of inadequate ADH secretion: pitfalls in diagnosis and therapy]

Euvolemic hyponatremia is most frequently caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Causes of SIADH-induced hyponatremia are myriad and include tumors, pulmonary diseases or central nervous system disorders. SIADH can also be induced by a broad spectrum of drugs such as antidepressants and antiepileptics. The unfavorable prognostic relevance of hyponatremia is often underestimated. SIADH therapy focuses on the treatment of the underlying disease. Thus, a thorough differential diagnostic assessment of the genesis of SIADH is crucial. Therapy options for euvolemic hyponatremia include fluid restriction, administration of hyperosmolar saline solution in case of severe symptoms, or therapy with tolvaptan. Tolvaptan is a selective, oral vasopressin-V2-receptor-antagonist that inhibits ADH-induced retention of electrolyte-free water in the connecting duct of the kidney. This inhibition results in an increased serum sodium level. Close monitoring of serum sodium levels and volume status is imperative, especially during the initial phase of therapy. Fluid restriction is unnecessary during tolvaptan therapy; a previously prescribed fluid re-striction should be stopped when therapy begins. Treatment with tolvaptan can often result in a rapid and controlled improvement of the symptoms. Different cases presented in this article illustrate the diversity of SIADH in clinical practice relating to its diagnosis and its therapy as well as difficulties in identifying the underlying cause in clinical practice.