Syndrome of inappropriate antidiuretic hormone caused by continuous lumbar spinal fluid drainage after transphenoidal surgery.

A 53-year-old acromegalic woman had cerebrospinal fluid rhinorrhoea following transphenoidal surgery for a pituitary microadenoma. A continuous lumbar spinal fluid drainage catheter was inserted and on the sixth postoperative day, she developed hyponatremia with features of syndrome of inappropriate antidiuretic hormone (SIADH) requiring hypertonic saline administration. Over-drainage is potentially hazardous and close biochemical monitoring is required. To our knowledge, this is the first reported case of SIADH caused by continuous lumbar drainage in an adult.