SAT213 Post-parathyroidectomy Acute Pseudogout Flare-up; A Case Report

Disclosure: S. Rabiei: None. V. Kantorovich: None. Introduction: Acute post-parathyroidectomy pseudogout has been reported in the early post-operative. Although the exact mechanism is unknown, accepted theories include decreased solubility of calcium pyrophosphate and unbalanced equilibrium between production and hydrolysis of inorganic phosphate. We present a patient who developed an acute pseudogout attack after parathyroidectomy. The Case: Patient is a 45-year-old male with a history of nephrolithiasis who presented to outpatient clinic with a right-sided neck mass that has been present for several years with recent increase in size. He reported unintentional weight loss (25 pounds) and night sweats. On physical examination, a right lateral neck mass measuring 6 x 4 cm was noted. CT scan of the neck demonstrated a complex mass with calcification. Serum calcium (Ca), phosphorus (P), potassium (K), and alkaline phosphatase levels were 17.2 mg/dL, 1.8 mg/dL, 2.6 mmol/L, and 1,782 U/L, respectively. Serum intact parathyroid hormone (iPTH) was 3,341 pg/mL. The patient was then admitted. He received intravenous fluid, zolindronic acid, and started on vitamin D supplementation in preparation for surgery. Pre-operative CT scan of the chest, abdomen, and pelvis was concerning for metastatic disease (retroperitoneal lymphadenopathy, multiple bilateral lung solid nodules, liver, kidney and bone lesions). The patient underwent complete resection of the tumor. Intra-operative frozen section confirmed parathyroid tumor with atypia. Twenty-minute post-excision iPTH was 476 pg/mL. In the early post-operative period, serum Ca level was reduced to 7.5-8.5 mg/dL and oral Ca and calcitriol supplementation were administered. However, serum PTH reached levels as high as 900 pg/mL. Post-operative MRI demonstrated benign liver and kidney lesion with non-visualization of the previously reported retroperitoneal lymph nodes and pulmonary nodules on the CT.A few days later, the patient complained of bilateral knee pain. Serum Ca, P, and PTH levels were 7.9 mg/dL, 3.0 mg/dL, and 861 pg/mL, respectively. The skeletal survey revealed diffuse osseous metabolic process with scattered lucent osseous lesions compatible with osteitis fibrosa cystica/brown tumors as well as chondrocalcinosis of knees and hand joints. Prednisone was started for treatment of presumed acute CPPD attack with subsequent significant resolution of patient’s joint pain. Discussion: This case demonstrated the importance of thorough evaluation of musculoskeletal complaints in patients with hyperparathyroidism. Bone and joint pain in patients with hyperparathyroidism is common and is most often the result of high bone turnover. However, other etiologies including acute pseudogout should be contemplated in order to provide the appropriate treatment. Post-parathyroidectomy acute pseudogout attack should generally be treated in the same way as in the general population. Presentation: Saturday, June 17, 2023