8106 An Uncommon Cause Of Hyperparathyroidism: A Case Report

Abstract Disclosure: A. Calderon: None. M.C. Aguilera: None. A. Kansara: None. Introduction: Parathyroid adenomas are the most common cause of primary hyperparathyroidism. Imaging techniques to locate parathyroid adenomas and hyperplasia include U/S (Sensitivity: 72%-89%), Sestamibi Tc-99 (Sensitivity of 68-95%), and 4D CT scan (Sensitivity of 80%). Combined imaging modalities increase sensitivity to 95%. We describe a case of symptomatic primary hyperparathyroidism with rapid development of hypercalcemia, and conflicting imaging findings. The final diagnosis was made after surgery and pathology review. Case presentation: A 76-year-old man with a history of hypertension, Parkinson’s disease, and prostate cancer was admitted due to a calcium level of 13 mg/dL (8.0 - 10.2 mg/dl) on routine blood tests. He had complained of progressive fatigue and constipation, attributed to Parkinson’s Disease. Five months prior his calcium was 9.7 mg/dL. Hydrochlorothiazide was discontinued due to hypotension after two months. Blood tests in the hospital showed a corrected calcium of 12.5 mg/dL, phosphorus of 1.7 (2.4 - 4.5 mg/dl), PTH of 195 (15 - 65 pg/ml), with normal vitamin D and undetectable PTHrP. A U/S of the neck showed a 0.4 x 0.5 cm cystic mass in the right-inferior pole of the thyroid. A 4D CT scan of the neck showed a non-enhancing 0.9 x 7 x 1 mm mass in the same location, and a 7 x 4.7 x 4.8 mm mildly enhancing mass in the left lower pole of the thyroid. A parathyroid nuclear scan did not identify a parathyroid adenoma. He underwent minimally invasive parathyroidectomy and was found to have a 3.2 cm enlarged and cystic right inferior parathyroid gland weighing 792 mg. Frozen section showed hypercellular parathyroid with cystic and fibrotic changes. The PTH level dropped 59% after removal of the right cystic mass. The left inferior mass identified on CT scan was identified as normal thyroid tissue. Conclusions: Parathyroid cysts are uncommon neck masses and represent less than 5% of causes of all neck masses. They can be divided into functional and non-functional. Large retrospective studies have shown that about 5% of patients manifest as classic hyperparathyroidism, whereas the most common presentation was neck mass (40%). Identification of parathyroid cysts through imaging can be challenging. In our case, the patient presented with symptomatic and rapidly progressive primary hyperparathyroidism, and imaging findings that were discordant among ultrasound, 4DCT scan and Sestamibi Tc-99 scan. The final surgical and pathology reports identified a large parathyroid cyst. This case emphasizes the variable clinical and imaging behavior of parathyroid cysts, imposing a puzzling medical challenge. Presentation: 6/3/2024