RESUMEN
BACKGROUND: The anti-natriuretic properties of growth hormone (GH) are well established. Growth hormone deficiency (GHD) results in salt and water depletion and studies confirm that replacement leads to sodium and vasopressin-mediated water retention in patients with intact posterior pituitary function. METHODS: We report the case of a 20-year-old male patient with septo-optic dysplasia, fixed cranial diabetes insipidus (DI) and an abnormal thirst threshold. With careful parental support, his sodium levels remained stable for many years on a fixed dose of DDAVP and a supervised fluid intake of 2.5 l/day. Several years after the original diagnosis, he was found to be ACTH deficient and following commencement of hydrocortisone replacement therapy became hypernatraemic. A new sodium homoeostasis was established with a higher dose of DDAVP. Subsequently, he developed symptoms typical of GHD and, after biochemical confirmation, GH replacement was commenced. RESULTS: There was an immediate clinical improvement (increased alertness, improved concentration) but severe hypernatraemia developed (peak 169 mmol/l) necessitating revision of his desmopressin and fluid intake regimen. CONCLUSION: Most GHD patients have intact posterior pituitary function. This case report highlights the powerful anti-natriuretic properties of GH. Endocrine physicians should be alert to this in patients with fixed DI and an abnormal thirst threshold.