THU404 Classical Symptoms Masquerading As A Surprising Clinical Picture

Disclosure: A. Syal: None. Y. Arya: None. S. Teja Sathi: None. J. Prater: None. Introduction: Primary hyperparathyroidism commonly presents in the setting of a parathyroid adenoma or hyperplasia, although it can rarely be caused parathyroid carcinoma, often accounting for <1% of cases. Markedly elevated PTH levels, along with predominant uniglandular involvement should increase the suspicion of an underlying parathyroid carcinoma, given that multiglandular involvement is rarely encountered. Surgical resection with histopathological confirmation remains the mainstay of diagnosis. Case presentation: We describe the case of a female in her late 50s who was brought to the emergency department by her family with complaints of altered mental status, hallucinations, delusions, anxiety, increased urination, constipation, and decreased appetite for the past month. Her laboratory evaluation was significant for hypercalcemia with a corrected calcium of 13.4 mg/dL. She was started on intravenous fluids and calcitonin, with improvement in her clinical condition. Further workup for her hypercalcemia revealed that the serum parathyroid hormone (PTH) was significantly elevated at 1846.4 pg/mL (normal low: 9, normal high: 73). Her serum phosphorus was low, and 25-hydroxy vitamin D was high-normal. This was consistent with a picture of primary hyperparathyroidism. The severely elevated PTH raised concern for parathyroid carcinoma, a rare clinical entity. The patient underwent a nuclear medicine parathyroid scan (technetium 99m sestamibi), which revealed abnormal focal uptake in the inferior right thyroid bed. Ultrasound of the neck revealed a hypoechoic avascular nodule inferior to the right thyroid lobe corresponding to the area of increased sestamibi activity on nuclear medicine scan. After much discussion with the patient’s family, surgical intervention was deferred to a later date, with a focus on stabilization in the acute setting. The patient was started on cinacalcet for her hypercalcemia. Bisphosphonates were initially held in anticipation for surgery but were eventually started. Discussion: Parathyroid carcinoma is a rare malignancy, which can occur both sporadically and as part of the hereditary hyperparathyroidism-jaw tumor syndrome. In clinical practice, subtle clues which increase the suspicion for a parathyroid carcinoma include severely elevated PTH, sometimes up to 10 times the upper limit of normal, increasing adenoma size, and a presentation outside of the commonly inherited MEN-1 syndromes.[1] We rely solely on post-operative pathology to establish the diagnosis of parathyroid carcinoma, given that there are no well-defined features or criteria that can establish the diagnosis on imaging. References: 1.Singh Ospina N, Sebo TJ, Thompson GB, et al. Prevalence of parathyroid carcinoma in 348 patients with multiple endocrine neoplasia type 1 - case report and review of the literature. Clin Endocrinol (Oxf). 2016;84(2):244-249. Presentation: Thursday, June 15, 2023