Breast cancer presenting with the syndrome of inappropriate secretion of antidiuretic hormone after simple mastectomy.

A 71-year-old woman showed disorientation 7 days after simple mastectomy for right breast cancer. Computed tomography of the brain was normal. The level of serum sodium was very low (110 mEq/l), while the urine sodium level was normal. The osmolality of urine was higher (342 mosmol/kg) than that of serum (220 mosmol/kg). These data suggested a syndrome of inappropriate secretion of antidiuretic hormone. A fluid restriction, infusion of hypertonic saline and administration of diuretics gradually increased the level of serum sodium. Subsequently, disorientation disappeared. This is a rare case of the syndrome of inappropriate secretion of antidiuretic hormone caused by simple mastectomy, a relatively minor surgical procedure.