Calcium and Parathyroid USMLE Step 1 Practice Question
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?
Answer choices
- AExcess cortisol leading to osmotic diuresis
- BSIADH due to ectopic ADH production
- CCompulsive water drinking with intact ADH axis
- DCollecting duct unresponsiveness to vasopressinCorrect answer
- EAutoimmune destruction of vasopressin secreting neurons
- FPrimary polydipsia with secondary nephrogenic diabetes insipidus from chronic hypernatremia
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