SAT194 A Rare Case Of Untreated Primary Hyperparathyroidism With Extremely High PTH And Lytic Bone Lesions

Disclosure: M. Shah: None. K. Akinola: None. M. Bollineni: None. S.A. Milan: None. S. Challagulla: None. Background: Primary hyperparathyroidism (PHPT) typically presents with PTH levels two times above the upper limit of normal. Given the increase in routine calcium measurements, PHPT is usually diagnosed and treated early and skeletal complications are not frequent at presentation. We present a case of PHPT with severely elevated PTH levels and bone lesions mimicking metastatic disease. Clinical Case: A 30-year-old male with a history of untreated primary hyperparathyroidism presented with severe chest wall pain and abdominal pain. Initial laboratory tests revealed a calcium level of 13.3 mg/dL (normal 8.6 to 10.5 mg/dL), alkaline phosphatase (AP) of 747 IU/L (normal 24 to 130 IU/L), and PTH of 2485 pg/mL (normal 9-77 pg/mL). The patient was diagnosed with primary hyperparathyroidism years before this presentation, but was lost to follow up due to lack of insurance. His PTH was first noted to be elevated in 2013 at 266 pg/mL. CT of the chest, abdomen, pelvis showed a 2.8 x 3.0 x 3.3 cm anterior mediastinal mass and diffuse mixed lytic and sclerotic bone lesions consistent with metastatic disease. The patient underwent further imaging with CT 4D parathyroid which revealed a 1.1 cm left inferior thyroid nodule and an anterior mediastinal mass of unclear etiology. Given the high concern for malignancy, a biopsy of the mediastinal mass was performed and returned as hypercellular parathyroid tissue with no atypia. Bone biopsies of the sclerotic lesions of the iliac crest were consistent with osseous tissue with prominent bone remodeling and fibrous tissue; no neoplasm was seen. He was treated with IV fluids and zoledronic acid during this work up which only temporarily improved his high calcium levels. He was then placed on cinacalcet prior to surgery. He ultimately underwent resection of the anterior mediastinal mass and left inferior parathyroid gland via a cervical approach. The patient’s preoperative PTH level was 3455 pg/mL and decreased to 209 pg/mL immediately after resection. Resection of the other parathyroid glands was not done due to the high risk of postoperative hypocalcemia. Pathology of both lesions returned as intrathymic parathyroid adenoma with focal fibrosis. Postoperatively, the patient developed symptomatic hypocalcemia as low as 6.4 mg/dL. He required IV and oral calcium for approximately 3 weeks postoperatively, consistent with hungry bone syndrome. He was discharged on an oral regimen of calcium supplementation. Discussion: Long standing untreated PHPT can present with severely elevated PTH levels and skeletal manifestations commonly mistaken for metastatic lesions. As in this case, parathyroidectomy was the only effective treatment. However, it can be complicated by hungry bone syndrome, especially in a patient with significant bone remodeling as evidenced by high AP and lytic bone lesions. Presentation: Saturday, June 17, 2023