8063 Cystic Parathyroid Adenoma: A Rare Cause Of Severe Hypercalcemia

Abstract Disclosure: M. Owrangi: None. F. Hasan: None. Introduction: Parathyroid adenomas are the most common cause of primary hyperparathyroidism, but within this category, a rare subtype exists - cystic parathyroid adenomas (CPAs). Comprising only 0.5-1% of all parathyroid lesions, CPAs present unique diagnostic and therapeutic challenges. We report a case of a female patient presenting with severe hypercalcemia caused by a CPA. Case presentation: A 44-year-old African American female with a history of nephrolithiasis presented with abdominal pain and signs of dehydration. Labs were remarkable for serum calcium 13.2 mg/dL, albumin 4.0 g/dL, phosphorus 1.8 mg/dL, iPTH 617.7 pg/mL, 25-OH vit D 12.1 ng/mL, creatinine 0.85 mg/dL. She was initially resuscitated aggressively with IV fluids resulting in an improvement in serum calcium level to 10.3 mg/dL. Thyroid US showed a cystic nodule deep to the left thyroid lobe. Sestamibi parathyroid scan was consistent with a left superior parathyroid adenoma. She underwent 2 gland parathyroidectomy 3 months after the initial presentation. Intraoperatively serum PTH decreased by 91% after resection of the 2 parathyroid adenomas. Pathology confirmed the presence of 2 parathyroid adenomas, the larger one measuring 2.8 cm and weighing 3.8 g. Discussion: We describe a case of a middle-aged female presenting with severe hypercalcemia due to CPA. Her initial presentation was concerning for parathyroid carcinoma given the severity of hypercalcemia. However, the radiologic findings, coupled with surgical pathology, indicated that she had CPA. CPAs can be either functional, causing primary hyperparathyroidism (PHPT) with elevated serum calcium levels, or non-functional, remaining asymptomatic. Clinical features of PHPT associated with CPAs are similar to those with solid adenomas and include fatigue, GI symptoms, nephrolithiasis, bone pain, and neuropsychiatric manifestations. However, CPAs may exhibit certain distinct presentations: i) higher pre-operative serum calcium levels; and ii) increased risk of symptomatic hypercalcemia. Despite their rarity, CPAs deserve special attention due to their unique presentation, challenging diagnosis, and potential for severe hypercalcemia. Surgical parathyroidectomy is the definitive treatment for functional CPAs. Accurate localization and complete excision of the adenoma are crucial to avoid recurrence. Most CPAs occur in the fourth and fifth decade of life and are more common in women (female to male ratio of 2.5:1). 65-85% of cases are located in the neck and the majority arise from the inferior parathyroid glands and are left-sided, and may very rarely be intrathyroidal. Presentation: 6/2/2024