Initial and postoperative hyponatremia associated with pituitary adenoma: a case report.

This 67 year-old man experienced 3 episodes of symptomatic hyponatraemia. Radiological examination revealed a sellar lesion and the tumour was removed via the transsphenoidal route. Thereafter, he simultaneously developed intractable diabetes insipidus and serious hyponatraemia with persistent natriuresis. His level of atrial natriuretic peptide was not significantly elevated, however, his plasma aldosterone concentration was low. The oral administration of salt gradually improved his hyponatraemia as well as the coincident symptoms. By the administration of a mineralocorticoid, fludrocortisone acetate, we succeeded in maintaining his serum sodium level without salt replacement. We discuss the mechanism(s) and treatment of hyponatraemia associated with pituitary tumour.