Adipsic hypernatraemia is an uncommon disorder in childhood caused by a defect in the osmoregulation of thirst, leading to impairment of water homeostasis and chronic hyperosmolality of body fluids. Adipsia is often associated with an abnormality in osmoregulated vasopressin secretion due to the close proximity of the hypothalamic osmoreceptors that control thirst with those regulating vasopressin secretion. Hypothalamic lesions of diverse aetiology (vascular abnormalities, neoplasms, granulomatous diseases, trauma etc.) have been described in this syndrome. We report a 12-year-old boy with evident weight loss due to hypernatraemic dehydration with a selective defect in osmoregulation of thirst and normal vasopressin secretion with no demonstrable structural lesion. To date, only six paediatric patients with this condition have been described in the literature.
Conclusion: Hypothalamic adipsic hypernatraemia syndrome must be suspected when a dehydrated patient denies thirst. The study of antidiuretic function is necessary because the osmoregulation of vasopressin secretion could be altered.