SAT188 Atypical Parathyroid Adenoma: A Diagnostic Challenge Of Primary Hyperparathyroidism

Abstract

Abstract Disclosure: S. Bendaram: None. L. Dulipsingh: None. Introduction: Atypical parathyroid adenomas(APA) are parathyroid neoplasms with some atypical histological features and of indeterminate malignant potential. They may occur sporadically or as a part of hereditary syndromes and contribute to 1.2-1.3% cases of Primary Hyperparathyroidism (PHPT). Here, we present an interesting case of hypercalcemia secondary to PHPT due to an underlying APA. Case Presentation: 28 year old white female with no known significant past medical history presented to ED with symptoms of nausea, vomiting and dizziness on standing. Physical examination was unremarkable except for dry mucous membranes and decreased bowel sounds. Initial labs revealed a total calcium of 19.6 mg/dl (8.4-10.2), PTH of 1161pg/ml (10-65), creatinine 1.2mg/dl (0.5-1.0), albumin 5.0 g/dl (3.5-5.0), ionized calcium 2.37 mmol/L (1.19-1.35), phosphorus 3.4 mg/dl (2.5-4.5), magnesium 1.6 mg/dl (1.7-2.8) TSH 0.51 uIU/ml (0.35-5.5), 25-hydroxy Vitamin D 24 ng/ml (30-100),1,25-dihydroxy Vitamin D 68 pg/ml (20-79) and PTHrP 19 pg/ml (11-20). Family history was negative for hypercalcemia, hyperparathyroidism, fragility fractures, pancreatic disease or any genetic syndromes. Inpatient treatment included IV fluids, 2 doses of calcitonin and Pamidronate 60 mg IV. Subsequently, over the hospital course, calcium improved to 11.9 mg/dl with improvement in her symptoms and she was discharged home. 24-hour urine calcium checked on an outpatient visit, after vitamin D replacement, revealed low urine calcium of 31 mg/24 hr. Ultrasound Thyroid demonstrated a 3.7 cm mass inferior to the right hemithyroid, suspicious for parathyroid adenoma versus abnormal lymph node. CT Parathyroid with and without contrast revealed normal thyroid and bilateral inferior parathyroid adenomas, right larger than left. She underwent en-bloc resection of right thyroid and right inferior parathyroid gland with final pathology showing atypical parathyroid adenoma, without evidence for obvious parathyroid carcinoma or metastatic disease. Genetic testing for a total of 53 genes including MEN, BRCA1, BRCA2 were negative. PTH levels normalized post-surgery. Conclusion: Atypical Parathyroid Adenomas have a clinical and biochemical profile more severe that the typical adenomas and, to some extent, similar but less severe to that of patients with parathyroid carcinoma, creating an overall diagnostic challenge. The molecular mechanisms are unclear, with germline CDC73 mutations appearing to be the most common defect. Due to uncertain malignant potential, a close and careful monitoring is recommended for these patients. Presentation: Saturday, June 17, 2023