Endocrine Abstracts

JOINT81

Background: Giant parathyroid adenomas (GPAs) are a rare cause of primary hyperparathyroidism, and are characterized by adenomas that weigh >3.5g. The large size and higher calcium levels of GPA may mimic parathyroid carcinomas.

Clinical Case: A 43-year-old female was referred to the Endocrinology for hypercalcemia, detected after evaluation for recurrent calculi was performed. Initial laboratory findings revealed adjusted serum calcium of 3.34mmol/l, albumin of 41g/l, and phosphate 0.5 mmol/l. On systems query, she denied polyuria, polydipsia, dysuria nor loin-to-groin pain. She had no bone pain, jaw pain, abdominal pain, dyspepsia, and constipation, constitutional symptoms or mood changes. She was not on calcium supplements, lithium or thiazide. Of note, she had a history of bilateral recurrent renal calculi treated with medical expulsive therapy. On examination, she was well hydrated, and did not have neck masses, or palpable lymph nodes. Systemic examination was unremarkable. Inpatient management of severe hypercalcemia included aggressive intravenous hydration, subcutaneous calcitonin and intravenous pamidronate. A diagnosis of primary hyperparathyroidism was made, complicated by renal calculi, low bone density, and stage 3A CKD. Parathyroid carcinoma was initially considered in view of her significantly elevated PTH levels. Due to her young age of onset, familial PHPT was considered. A screen for symptoms associated with multiple endocrine neoplasia (MEN) syndrome was negative. Neck ultrasound demonstrated a large, lobulated, hypoechoic mass posterior to the left hemi-thyroid (5.1 × 1.7 × 1.7 cm). Technetium-99m labelled sestamibi localized the left hyperfunctioning parathyroid tissue. Early definitive left parathyroidectomy was performed, and histology revealed a parathyroid adenoma with no features of malignancy. She did not have hypocalcemia post-operatively. During follow-up over 3 years, she has remained normocalcemic, with improvements in bone density.

Conclusions: GPA appears to be a genetically distinct entity compared to parathyroid adenomas and carcinoma. (1) While no malignant transformation has been noted in the literature, patients with atypical adenomas should be followed up because of the molecular resemblance to carcinomas. (2) As it is difficult to differentiate parathyroid carcinomas from giant parathyroid adenomas pre-surgically, a strong clinical index of suspicion of malignancy is important to avoid a misdiagnosis.

References: 1. Sulaiman L, Nilsson I, Juhlin C, Höög A, Larsson C, Hashemi J. Genetic characterization of large parathyroid adenomas. Endocr Relat Cancer. 2012;19(3):389–407.2. Spanheimer P, Stoltze A, Howe J, Sugg S, Lal G, Weigel R. Do giant parathyroid adenomas represent a distinct clinical entity? Surgery. 2013;154(4):714–19.