Primary Hyperparathyroidism From Ectopic Parathyroid Adenoma in a Patient With Bilateral Slipped Capital Femoral Epiphysis

Background: Primary hyperparathyroidism has been reported in 13 pediatric patients presenting with slipped capital femoral epiphysis (SCFE), but never in patients with ectopic parathyroid adenoma [1]. Case report: A 12-year-old boy with obesity (BMI 99(th) percentile) and autism spectrum disorder presented with a limp and was found to have bilateral SCFE. Calcium was elevated to 12.3 mg/dL (reference range 8.0–10.5) with phosphorus of 3.2 mg/dL (3.0–5.7), alkaline phosphatase 775 units/L (40–360), tubular reabsorption of phosphorus 89% (&gt 95%), 25OH-vitamin D 12.1 ng/mL (30–80), 1,25OH-vitamin D 246.6 pg/mL (19.9–79.3), and PTH 1191 pg/mL (10–65). He had significant neuropsychiatric agitation but denied constipation, polyuria, and other symptoms of hypercalcemia. He had in situ pinning of the SCFE bilaterally and was hyperhydrated with minimal improvement in his calcium level. Neck ultrasound revealed no parathyroid adenoma. He was discharged on cholecalciferol 1000 IU daily with plans for outpatient Tc-99m Sestamibi scintigraphy. Following discharge, he developed significant nausea, did not tolerate the cholecalciferol, and was non-weight bearing. Repeat labs and imaging 5 days later demonstrated calcium had risen to 16.7 mg/dL with phosphorus of 2.2 mg/dL. He was admitted and calcium improved transiently to less than 12 mg/dL with intranasal calcitonin therapy. Sestamibi and subsequent CT scan revealed a 2.7x1.6x1.9 cm ectopic parathyroid adenoma in the upper anterior mediastinum. He had thoracoscopic resection of the mass, which was revealed to be intrathymic, and PTH levels fell from 1613 pg/mL pre-operatively to 76 pg/mL 30 minutes post-resection. Post-operatively, he developed hungry bone syndrome with a calcium nadir of 7.6 mg/dL and phosphorus nadir of 1.6 mg/dL, which required oral calcium and calcitriol for 10 days. With normalization of his calcium, his neuropsychiatric symptoms improved. Pathology revealed a parathyroid adenoma. Conclusion: Primary hyperparathyroidism can be associated with SCFE and should be considered even in patients with traditional risk factors for SCFE, especially with bilateral disease. Pediatric patients with primary hyperparathyroidism and negative neck imaging should be further evaluated for ectopic parathyroid adenomas. References: 1. George, G.S., Raizada, N., Jabbar, P.K., Chellamma, J., Nair, A. Slipped Capital Femoral Epiphysis in Primary Hyperparathyroidism - Case Report with Literature Review. Indian J Endocrinol Metab. 2019 Jul-Aug;23(4):491–494.