Endocrine Abstracts

Adipsic diabetes insipidus (ADI) is a rare condition which has been reported following clipping of anterior communicating artery aneurysms, craniopharyngioma and brain trauma, but not with pituitary adenoma. We report a case of ADI following surgery for a pituitary macroprolactinoma. A 14-year-old boy presented with bitemporal hemianopia due to a large macroprolactinoma. Two debulking surgeries were performed without the development of diabetes insipidus. Following a third radical surgery, plasma sodium rose in the post-operative period to 157 mmol/l, after a diuresis of nine litres/24 h. He did not complain of thirst. He was resuscitated with intravenous dextrose and oral desmopressin. Hypertonic saline infusion caused a rise in plasma osmolality from 293 to 318 mOsm/kg, but plasma vasopressin levels remained undetectable (<0.3 pmol/l). Thirst ratings, measured by visual analogue scale, remained low (0.3 to 0.8 cm) and he drank only 400 mls of water (normal 1544±306 mls) in 30 min after infusion. These results confirmed ADI. A controlled reduction in mean arterial blood pressure from 93 to 66 mmHg using intravenous infusion of trimetaphan camsylate also failed to stimulate vasopressin secretion (<0.3 pmol/l throughout infusion). This boy therefore had absent osmoregulated thirst and vasopressin secretion and absent baroregulated vasopressin release. This combination of defects implies that the final surgery lesioned the osmoreceptors for thirst and vasopressin in the circumventricular organs and the supraoptic and paraventricular nuclei which synthesize vasopressin. This is the first report of ADI with absent osmoregulated and baroregulated vasopressin release following surgery for a pituitary adenoma.