A patient with Cushing's disease undergoes transsphenoidal surgery. Post-operatively, serum cortisol at 0800 h is 1.2 µg/dL and the patient develops nausea, hyponatremia and fatigue. Which statement about post-operative management is MOST accurate?
- A A post-op morning cortisol <2 µg/dL is consistent with remission and hydrocortisone replacement should be started ✓
- B Low post-op cortisol confirms surgical cure and glucocorticoid replacement should be withheld to test adrenal recovery
- C Bilateral inferior petrosal sinus sampling should be repeated to confirm remission
- D Desmopressin should be given to treat the hyponatremia
Correct answer: A. A post-op morning cortisol <2 µg/dL is consistent with remission and hydrocortisone replacement should be started
Explanation
Post-operative morning cortisol <2 µg/dL (or <50 nmol/L) is the most reliable early indicator of remission after transsphenoidal surgery for Cushing's disease, reflecting suppression of the HPA axis. These patients require hydrocortisone replacement until adrenal recovery occurs, which may take 6–18 months. Withholding replacement risks adrenal crisis. Desmopressin treats diabetes insipidus (hypernatremia/polyuria), not hyponatremia from secondary adrenal insufficiency.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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