Adipsic hypernatraemia without hypothalamic structural abnormality

We report a woman in her 20s with chronic, severe hypernatraemia and absent thirst perception; diagnosed with adipsic hypernatraemia without any hypothalamic structural abnormality. She presented with persistent hypernatraemia on multiple occasions, remaining asymptomatic throughout. Her urine was concentrated and her arginine vasopressin (antidiuretic hormone) response was preserved. Her medical history included midline facial defects (cleft lip and cleft palate), developmental delay, sensorineural hearing loss, chronic macrocytosis and a paternally inherited 15q25.2 duplication. Comprehensive investigations excluded arginine vasopressin deficiency (AVP-D), adipsic AVP-D, dehydration, salt overload and autoimmune and endocrine causes. A strict fluid intake regimen was implemented; this resulted in normalisation of serum sodium concentration, with episodes of mild hypernatraemia only when the regimen was not adhered to. This case highlights the fundamental role of thirst perception in osmoregulation, the importance of considering adipsia as a differential diagnosis for severe hypernatraemia and the critical role of structured fluid intake in management.