Syndrome of inappropriate antidiuretic hormone
secretion (SIADH) is characterized by excessive release of antidiuretic hormone from the posterior pituitary gland or another source. The increase in fluid retention often results in dilutional hyponatremia
in which the plasma sodium levels are lowered. SIADH may present with euvolemic hyponatremia with continued urinary sodium excretion. Urine osmolality is usually higher than serum osmolality. Very low serum sodium levels can lead to cerebral edema or seizures
. Hyponatremia must be slowly corrected to prevent osmotic demyelination syndrome
. Treatment for SIADH can include fluid restriction, salt tablets, IV hypertonic saline, diuretics, conivaptan, tolvaptan, or demeclocycline.