MON-087 Glucocorticoid Withdrawal State Presenting Late After Surgical Cure Of Cushing’S Disease With Severe Hypercalcemia

Abstract Disclosure: F. Loo: None. R. Lai: None. Introduction Glucocorticoid withdrawal syndrome (GWS) typically occurs days after successful surgical treatment of Cushing’s disease (CD) and presents with non-specific symptoms. We report a rare presentation of GWS with severe hypercalcemia occurring months after successful surgical treatment of CD, at time of recovery of the hypothalamic-pituitary-adrenal (HPA) axis. Case Report A 54-year-old woman with severe CD underwent transsphenoidal surgery with an early post-operative serum cortisol nadir of 93 nmol/L. After surgery, she received a tapering dose of glucocorticoids. At time of hydrocortisone discontinuation 4 months later, short Synacthen test demonstrated a baseline ACTH of 2 pmol/L, 0-minute cortisol of 297 nmol/L, and robust peak cortisol (60 minutes) of 798 nmol/L. 1 week later, the patient was hospitalized with symptoms of nausea, anorexia, and malaise. Repeat 8am cortisol was 363 nmol/L. Serum calcium (adjusted for albumin) was elevated at 3.83 mmol/L [2.15 - 2.50], phosphate 1.7 mmol/L [0.8 - 1.4], creatinine 114 umol/L [40-75] and 25-hydroxyvitamin D 51 mcg/L [30-100]. Parathyroid hormone (PTH) was suppressed at 1.3 pmol/L, PTH related peptide suppressed at 1.7 pmol/L [<4.2], and 1,25-hydroxyvitamin D also suppressed at 10 pg/mL [18-78]. Free thyroxine was 17 pmol/L [8-16] and thyroid stimulating hormone 5.68 mIU/L [0.45 - 4.50], not accounting for hypercalcemia. A negative myeloma panel and unremarkable 18-fluorodeoxyglucose positron-emission tomography (PET) CT scan excluded other causes of non-PTH-mediated hypercalcemia. Following initial treatment of hypercalcemia with hydration and intravenous pamidronate 30mg, the reinstitution of supraphysiological doses of glucocorticoids resulted in sustained improvement of serum calcium levels to 2.38-2.70 mmol/L in the following eight months to date. Discussion GWS usually develops following a rapid relative reduction of excess circulating glucocorticoid. The risk is heightened in treated CD patients with previously prolonged, severe hypercortisolism. Non-PTH-mediated hypercalcemia is an uncommonly reported presentation, and is characterized by elevated urinary calcium and hydroxyproline excretion, and a response to supraphysiological doses of glucocorticoid. Conclusion Treated CD patients with a recovered HPA axis may still present with GWS owing to a state of relative glucocorticoid insufficiency. Hypercalcemia is an atypical presentation. Presentation: Monday, July 14, 2025