12313 Parathyroid Carcinoma Presenting As Right Foot Pain And Swelling In A Young Male - A Case Report

Abstract Disclosure: F.E. Sorsona: None. L. Lopez: None. Parathyroid carcinoma is a rare cause of hyperparathyroidism that is challenging to diagnose. We report a case of parathyroid carcinoma with an unusual initial presentation of right foot pain and swelling in a young 26-year-old Filipino male. Physical examination revealed a palpable 1 x 1 cm mass with tenderness on his right foot. Initial work-up showed a persistently elevated serum ionized calcium (range: 1.7 - 2.19 mmol/L) with markedly high intact parathyroid hormone (1,890 pg/ml). A right foot x-ray revealed a lytic bone lesion on the 3rd metatarsal. Skeletal survey revealed diffuse lytic bone lesions. Comprehensive neck ultrasound showed a 4 x 1.6 x 2.5 cm complex nodule adjacent to the inferior pole of the left lobe of the thyroid gland with intralesional calcifications. A 4D CT scan showed a 3.3 x 2.2 x 2 cm hypervascular nodule inferior to the left thyroid lobe with early contrast washout, likely parathyroid in origin, and a possible brown tumor in the right fourth rib. Patient underwent parathyroidectomy with intraoperative PTH monitoring showing a marked reduction of intact PTH by 87% (235.9 pg/ml from 1,890 pg/ml), accompanied by reduction of serum ionized calcium. The histopathology reported parathyroid carcinoma highlighted by lymphovascular invasion, atypical round cells in sheets and nests, with enlarged, mildly pleomorphic, hyperchromatic nuclei and prominent nucleoli. Two months after surgery, normal serum ionized calcium was maintained with calcium supplementation with reported relief of right foot pain and swelling. The patient continues to follow up regularly for monitoring of treatment response. Presentation: 6/2/2024