Studies of acquired sustained hypernatraemia occurring in a diabetic patient.

We describe studies undertaken in a diabetic patient with acquired sustained severe hypernatraemia. Arginine vasopressin levels and thirst scores were grossly subnormal in the presence of marked hypernatraemia but arginine vasopressin increased normally under the influence of negative pressure-induced hypovolaemia. Despite very low levels of arginine vasopressin, polyuria was not a feature suggesting acquired renal hyper-responsiveness. This patient is an additional case of acquired osmoregulatory dysfunction, whose features do not fall neatly into previously described categories.