Hyponatremia and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

The syndrome of inappropriate ADH secretion (SIADH) also recently referred to as the 'syndrome of map propriate antidiuresis, is an often underdiagnosed cause of hypotonic hyponatremia resulting for instance from ectopic release of ADH in lung cancer or as a side effect of various drugs In SIADH, hyponatremia results from a pure disorder of water handling by the kidney, whereas external Na+ balance is usually well regulated Despite increased total body water only minor changes of urine output and modest edema are usually seen Renal function and acid base balance are often preserved while neurological impairment may range from subclinical to life threatening Hypouricemia is a distinguishing feature The major causes and clinical variants of SIADH are reviewed, with particular emphasis on iatro genic complications and hospital acquired hyponatremia Effective treatment of SIADH with water restriction aquaretics, or hypertonic saline + loop diuretics, as opposed to worsening of hyponatremia during parenteral isotonic fluid administration underscores the importance of an early accurate diagnosis and careful follow up of these patients (J Endocrinol Invest 33 671 682, 2010) (c) 2010 Editrice Kurtis