SAT-766 Role of 11C-choline PET/CT scan in a case of persistent hypercalcemia secondary to parathyroid hormone persistent elevation after removal of parathyroid adenoma

Abstract Disclosure: E. Mendez: None. M.I. Castillo: None. N. Shahid: None. A. Habouh: None. N.H. Shaaban: None. Background: Primary hyperparathyroidism (PHPT) is the leading cause of hypercalcemia in the outpatient setting and is known to target the skeletal and renal systems. Abnormal embryological migrations of the parathyroid glands give rise to a rare cause of PHPT, ectopic parathyroid adenomas. Due to the difficulty of localizing ectopic adenomas preoperatively, diagnosis and surgical treatment can be challenging. Clinical Case: A 55-year-old female presents for medical care of recently diagnosed hypercalcemia and hyperparathyroidism (HPT). Past medical history included hypertension (HTN), dyslipidemia, prediabetes, obesity, hypercalcemia, and HPT. On examination, her blood pressure was 135/93 mmHg (90/60-120/80), and her BMI was 38.69 (18.5-24.9). The patient denied classic symptoms of high calcium and usage of hydrochlorothiazide (HCTZ) or lithium. She was diagnosed with HPT when initial laboratory results showed calcium 11 mg/dL (8.6-10.4), albumin 4.6 g/dL (3.6-5.1), PTH 237 pg/mL (16-77), eGFR 102 mL/min/1.73m2 (> OR =60). Parathyroid sestamibi scintigraphy with planar and SPECT/CT and a full laboratory were ordered to check for parathyroid adenoma. The sestamibi scan showed no focal persistent abnormal uptake to suggest localization of a parathyroid adenoma. Posteriorly, a 4D parathyroid CT scan showed a 9x6 mm parathyroid adenoma immediately posterior to the lower pole of the right thyroid lobe and posterior to the plane of the right tracheoesophageal groove. The patient was put on losartan HCTZ 100/25 mg once a day and amlodipine 10 mg tablet daily for her HTN, which was controlled at <=120/80 mmHg throughout her follow-ups. Following the diagnosis of parathyroid adenoma, the patient was referred to surgical oncology and treated with minimally invasive radio-localized parathyroidectomy with laryngeal nerve integrity monitoring. In her follow-up in November 2023, after the parathyroidectomy, the patient significantly improved her blood calcium levels and PTH. However, on her follow-up 2 months later, her laboratory results showed elevated values for calcium at 10.6 mg/dL (8.6-10.4 mg/dL), calcium ionized at 5.9 mg/dL (4.65-5.25), and PTH 171 pg/mL (16-77). A 4D parathyroid CT scan in April 2024 showed no sign of new adenoma. In December 2024, an 11C-choline PET/CT Choline scan revealed two foci of increased choline uptake seen on the left lobe of the thyroid gland. The patient was diagnosed with ectopic parathyroid adenoma and is scheduled for surgical removal. Conclusion: Diagnosing ectopic parathyroid adenomas presents unique challenges, even with standard imaging. Advanced imaging techniques, such as 11C-choline PET/CT choline scans, are valuable tools in the screening process for detecting ectopic adenomas, where standard techniques may not be enough. In cases where surgery fails to resolve HPT or persistent hypercalcemia, ectopic adenomas should be considered. Presentation: Saturday, July 12, 2025