A positive desmopressin challenge test signifies which type of diabetes insipidus?

A positive desmopressin challenge test is indicative of centrally-mediated diabetes insipidus (DI). This type of DI occurs when there is a deficiency of antidiuretic hormone (ADH), or vasopressin, which is produced in the hypothalamus and stored in the posterior pituitary gland. Desmopressin is a synthetic analog of ADH and is used to assess the functionality of the kidneys in response to ADH.

When desmopressin is administered, individuals with centrally-mediated DI will typically show a significant decrease in urine output and an increase in urine osmolality, demonstrating that the kidneys can concentrate urine when sufficient ADH-like activity is present. This positive response suggests that the issue lies in the inadequate production of ADH from the brain rather than a renal resistance to ADH, which would be characteristic of nephrogenic diabetes insipidus, where the kidneys do not respond to ADH.

In the case of psychogenic DI, the underlying cause is behavioral, involving excessive fluid intake that leads to dilute urine production, and the desmopressin challenge would typically not yield a positive response. Similarly, gestational DI occurs during pregnancy and is due to increased breakdown of ADH, and