Pathogenesis of extracellular fluid abnormalities of hypothalamic hypodipsia-hypernatremia syndrome.

A 26-year-old man with hypothalamic hypodipsia-hypernatremia syndrome is reported, who presented with adipsia, hypernatremia, and impaired osmolality-mediated arginine vassopressin (AVP) secretion. A chorionic gonadotropin-secreting tumor was detected in the anterior hypothalamus and treated with external irradiation. After the treatment, hypernatremia persisted and was not corrected by fluid loading, osmolality-mediated AVP secretion remained impaired. Despite the absence of signs of hydropenia, hypovolemia was suggested by low blood pressure and elevated plasma indices of the renin-angiotensin system, and supported by blood volume determination. The plasma aldosterone concentrations were inappropriately low for the renin-angiotensin status. The plasma atrial natriuretic polypeptide (ANP) level was normal in spite of hypovolemia and increased more than double after fluid loading. Hypernatremia, primarily caused by hypodipsia and impaired osmolality-mediated AVP secretion, secondarily sustained ANP secretion and suppressed aldosterone release, which conceivably contributed to the development and perpetuation of hypovolemia in this patient.