Abstract
Disclosure: B.R. Ellison: None. S. Kafle: None. G. Mangu: None. R. Yatavelli: None. Introduction: Roux-en-Y gastric bypass (RYGB) frequently leads to calcium and vitamin D malabsorption, resulting in secondary hyperparathyroidism (SHPT) [1]. Persistent parathyroid stimulation may progress to tertiary hyperparathyroidism (THPT), sometimes requiring surgery. However, primary hyperparathyroidism (PHPT) can also develop in RYGB patients [2]. Recognizing overlapping hyperparathyroid etiologies is essential, as management strategies differ significantly. Case Presentation: A 68-year-old female with a history of RYGB (1991) presented in December 2020 with parathyroid hormone (PTH) 2481.7 pg/mL and corrected calcium 11.3 mg/dL. Laboratory testing revealed severe vitamin D deficiency (6.5 ng/mL), hypophosphatemia (2.1 mg/dL), and normal renal function. The extreme PTH elevation, surpassing typical SHPT levels, raised suspicion for an additional pathology, including PHPT, THPT, or parathyroid carcinoma. A neck ultrasound detected a large hypoechoic lesion inferior to the right thyroid lobe, and parathyroid scintigraphyconfirmed increased uptake in the right inferior parathyroid gland. In March 2021, surgical exploration revealed a 2.17 g right inferior parathyroid adenoma, which was excised. Intraoperative PTH dropped from 658 pg/mL to 41 pg/mL, with normalization of serum calcium (9.2 mg/dL). Vitamin D supplementation was continued, and PTH levels gradually improved over follow-up. Clinical Lessons: Although SHPT frequently follows RYGB, this case demonstrates that overlapping hyperparathyroid pathologies can occur, necessitating thorough evaluation to avoid misdiagnosis. In malabsorption states, markedly disproportionate labs or persistently elevated PTH—despite adequate SHPT management—should prompt suspicion for an additional hyperparathyroid process. Furthermore, the opposing effects of SHPT and PHPT on calcium homeostasis can obscure typical biochemical patterns, delaying recognition of dual pathology. Early identification of dual etiologies is essential to guide definitive treatment and prevent complications such as nephrolithiasis, osteoporosis, and cardiovascular disease. References: 1. Jin J, Strombom Y, Mattsson C, et al. Increases in PTH after gastric bypass appear to be of secondary nature. Obes Surg. 2020;30:1192-8. 2. Silverberg SJ, Bilezikian JP. Current issues in the presentation of hyperparathyroidism: proceedings of the Fourth International Workshop. J Clin Endocrinol Metab. 2014;99:3580-94. Presentation: Monday, July 14, 2025