Endocrine Abstracts

An 18 year old gentleman was first reviewed in our endocrine adolescent transition clinic. He had been under the care of the paediatricians since birth, where he initially presented with developmental delay. This triggered investigations which led to the diagnosis of septo-optic dysplasia. At aged 12 he developed cranial diabetes insipidus (DI) and secondary hypothyroidism. This was managed with intranasal DDAVP (20 ug BD) and thyroxine 125 μg. Due to an abnormal thirst threshold he was required to take up to 2.5 l/day of fluid to maintain sodium levels within the normal range. This was only achievable through the heroic efforts of his caring family. At that point his family were worried about his ‘lack of vitality’ and energy. Several 0900 h serum cortisol levels of <100 nmol/l were measured therefore he was commenced on hydrocortisone replacement (5 mg BD). This however caused him to become hypernatraemic (Na 151 mmol/l). His fluid ‘prescription’ and DDAVP dose had to be adjusted accordingly, until a new equilibrium was established. A previous glucagon stimulation test documented evidence of growth hormone deficiency (GHD). However treatment was not initiated until the family raised concerns of his increasing lethargy, somnolence and increasing central obesity, 6 months after starting hydrocortisone replacement. He was commenced on GH replacement (0.3 mg OD). Although this greatly improved his level of alertness and short term memory, it led to decompensation of his DI, resulting in severe hypernatraemia: peak Na169 mmol/l. Disturbance of sodium balance with GH had been predicted, but the extent was unexpected and required inpatient correction. Septo-optic dysplasia is a congenital condition characterised by optic nerve hypoplasia, hypopituitarism and other midline brain defects. The evolving nature of the various endocrinopathies over time makes management of sodium and water balance especially challenging. ACTH deficiency is known to cause hyponatraemia. This may have been partially masked DI, which was revealed when he was commenced on hydrocortisone. The sodium-water equilibrium was again disrupted when he was started on GH replacement. Patients with GHD have sodium and water depletion. When GH replacement is initiated, there is usually stimulation of thirst, triggering an increase in fluid intake to match the sodium retention to keep serum sodium concentrations constant. However, due to hypothalamic dysfunction in our patient, this compensatory mechanism was lost, resulting in severe hypernatraemia. This case highlights the complex nature of sodium homeostasis and the profound effects the anterior pituitary hormones can have on that delicate balance.