Thirst in diabetes insipidus: clinical relevance of quantitative assessment

Patients with cranial diabetes insipidus are unable to concentrate urine, and depend on thirst and water intake to prevent hypertonic dehydration. Using a visual analogue scale (0-10 cm) we studied osmotically stimulated thirst induced by hypertonic saline infusion in 15 patients with diabetes insipidus and 15 healthy controls. Plasma osmolality in the patients rose from 292 +/- 1 to 316 +/- 1 mOsm/kg (p less than 0.001), and 13 patients showed a progressive rise in thirst ratings (1.4 +/- 0.4 to 8.1 +/- 0.3 cm, p less than 0.001) with abolition of thirst by drinking, in a similar fashion to controls. Water intake following infusion was greater in patients than controls (p less than 0.001). Linear regression analysis of thirst and plasma osmolality showed no difference in the osmotic threshold for thirst onset, or the sensitivity of thirst osmoreceptors, between 13 of the patients and the control group. One patient was shown to be hypodipsic and compulsive water drinking was demonstrated in another: abnormal thirst perception caused abnormalities of salt and water balance in these two patients. Most patients with cranial diabetes insipidus have normal thirst mechanisms, though clinically significant hypodipsia or hyperdipsia may co-exist with vasopressin deficiency.