A 37-year-old woman with bipolar disorder on lithium presents with several months of polyuria and polydipsia. Vital signs show BP 128/82, HR 88, RR 16, temperature 37°C, and SpO2 98%. Serum sodium is 148 mEq/L. Water deprivation test fails to increase urine osmolality above 280 mOsm/kg, and subsequent desmopressin administration produces minimal change in urine concentration. There is no recent history of head trauma. Which of the following best explains these findings?

1. A)Excess cortisol leading to osmotic diuresis
2. B)SIADH due to ectopic ADH production
3. C)Compulsive water drinking with intact ADH axis
4. D)Collecting duct unresponsiveness to vasopressinGABARITO
5. E)Autoimmune destruction of vasopressin secreting neurons