[Hyponatremia in isolated deficiency of adrenocorticotropic hormone: role of a decrease in aldosterone secretion independent of antidiuretic hormone excess].

We report a case of 47-year-old woman with an isolated deficiency of adrenocorticotropic hormone. She was admitted complaining of fatigue and frequent loss of consciousness. The patient developed severe hyponatremia (100 mEq/l) after five days of the admission. Her plasma renin activity and plasma aldosterone concentration were low though she was dehydrated. After the treatment of dehydration, plasma osmolality was low but high plasma antidiuretic hormone (ADH) level sustained. Both high urinary sodium excretion and low urinary aldosterone excretion still remained after one month of replacement therapy with prednisolone. But, glomerular filtration rate and a response of urinary volume to acute water loading were normalized. These results suggested that severe hyponatremia of the patient was caused by an inappropriate secretion of ADH and suppression of renin-aldosterone system. We consider the suppression of renin-aldosterone system was partially independent of an inappropriate secretion of ADH.