Severe hyponatremia caused by hypothalamic adrenal insufficiency

A 60-year-old woman was admitted with severe hyponatremia, Basal values of adrenocorticotropic hormone (ACTH), thyroid hormone and cortisol were norma l on admission. Impairment of water diuresis was observed by water loading test. Initially, we diagnosed her condition as the syndrome of inappropriat e secretion of antidiuretic hormone (SIADH), By provocation test, we finall y confirmed that the hyponatremia was caused by hypothalamic adrenal insuff iciency. The basal values of ACTH and cortisol might not be sufficient to e xclude the possibility of adrenal insufficiency. Therefore, it is necessary to evaluate adrenal function by provocation test or to re-evaluate it afte r recovery from hyponatremia.