Hyponatremia due to cerebral salt-wasting syndrome. Combined cerebral and distal tubular lesion.

A 76-year-old white man was evaluated for a syndrome of hyponatremia, hypotension, and high urinary sodium excretion. There was evidence of inappropriate secretion of antidiuretic hormone and renal salt wasting in the presence of a normal glomerular filtration rate. He had a distal tubular acidification defect and unresponsiveness to standard doses of mineralocorticoids. The renin aldosterone axis was normal, as were thyroid and adrenal function. The patient could not dilute the urine, nor excrete a standard water load. Renal concentrating ability was normal, but there was no additional response to exogenous vasopressin. With modest salt restitution, the patient continued to lose large quantities of sodium in the urine, resulting in severe postural hypotension. Renal biopsy showed normal glomeruli with distinct degeneration of the distal tubules. There was no evidence of an acute inflammatory interstitial nephritis. The patient did not respond to therapeutic doses of mineralocorticoid (fludrocortisone), but treatment with water restriction, increased salt intake, and large doses of mineralocorticoids resulted in a normal serum sodium level and blood pressure. This case falls in the category of "cerebral salt wasting" syndrome. The cause was a combination of idiopathic secretion of antidiuretic hormone and distal tubular degeneration resulting in pseudohypoaldosteronism.