ATYPICAL RECURRENCE OF PARATHYROID CARCINOMA FOLLOWING INFLIXIMAB THERAPY IN A PATIENT WITH ULCERATIVE COLITIS.

Objective: Parathyroid carcinoma (PTC) has a high rate of recurrence, which typically occurs within 5 years of diagnosis involving locoregional sites. Immunosuppressive therapies pose a theoretical increased risk of malignancy. We report an atypical case of PTC recurrence in a patient receiving infliximab therapy for ulcerative colitis (UC).

Methods: Main diagnostic tests performed included calcium and parathyroid hormone (PTH) levels, computed tomography, and a venous sampling study.

Results: A patient with PTC, who was "cured" by parathyroidectomy, presented with recurrent hypercalcemia 21 years after his initial diagnosis. He had recently been diagnosed with UC and was started on infliximab. His serum PTH level was elevated. After negative routine neck imaging studies and sestamibi scan, he underwent selective venous sampling with PTH measurements, which localized the source lesion to the thoracic wall. Subsequent imaging showed multiple left lung and pleural nodules, which were surgically resected. Hypercalcemia abated after surgery, but quickly returned and was recalcitrant to treatment with cinacalcet and zoledronic acid. Further imaging demonstrated recurrent lung metastases, some along the left diaphragm. He underwent 2 additional surgical resections, after which PTH and calcium levels normalized. Infliximab was replaced with vedolizumab for treatment of UC.

Conclusion: Atypical presentation of PTC may occur in the context of immunosuppressive therapy. Venous sampling with PTH measurements can aid in localization of atypical metastatic PTC. Additional surveillance for PTC recurrence may be prudent following the initiation of immunosuppressive therapy in patients with a history of PTC.