ELECTROLYTE QUIZ

Answer: E

The Question

A 45-year-old female underwent transsphenoidal resection of a pituitary adenoma 1 week ago. Immediately postoperatively she developed severe polyuria and was started on DDAVP. She returns with change in mental status, has a seizure in the emergency room, and is found to have a serum sodium of 114 mEq/L.

Which of the following statements is TRUE?

A. Her postoperative condition was almost certainly misdiagnosed and she should never have been treated with DDAVP

B. She currently has diabetes insipidus

C. Her hyponatremia now is most likely due to central (pituitary) hypothyroidism

D. Her hyponatremia is primarily due to psychogenic polydipsia

E. She is at risk of developing diabetes insipidus 

Explanation

Pituitary surgery often causes a triphasic diabetes insipidus pattern. Initial injury to the pituitary causes acute inhibition of vasopressin secretion leading to polyuria, that lasts 4-5 days. DDAVP is appropriate in severe cases. This is often followed by a second, antidiuretic phase, lasting 5-6 days, which is thought to be due to leakage of vasopressin from degenerating neurons. Failure to recognize this possibility, and appropriately reduce or discontinue DDAVP, can result in serious hyponatremia, as in this case. In the third phase, the vasopressin stores become exhausted. If the cells cannot make new vasopressin, diabetes insipidus returns permanently.


(Source: Dr. Alan Yu, Director, Kidney Institute, University of Kansas Medical Center)