SUN-934 A Rare Case of Hyperparathyroidism - Parathyroid Carcinoma, Atypical Adenoma, or Both?

Introduction: Parathyroid carcinoma (PC) is a rare endocrine malignancy. It accounts for <1% cases of primary hyperparathyroidism (PHPT). We present a rare case of concurrent PC and atypical parathyroid adenoma (PA). Case presentation: A 72-year-old woman presented with 1-week history of generalized weakness, confusion, and auditory hallucinations. Her medical history was significant for PHPT known for 5 years, CAD and CHF. The patient appeared mildly volume depleted and was tachycardic (105/min). The rest of her physical exam was unremarkable. Calcium (Ca) was 15.1 mg/dL (8.4–10.2 mg/dL) and intact PTH 451.9 pg/mL (12–88 pg/mL). Her condition improved with aggressive fluid replacement, pamidronate, and cinacalcet. A sestamibi scan revealed increased uptake of bilateral parathyroid tissue. Fine needle aspiration (FNA) revealed PA. Surgical treatment was postponed for control of cardiac comorbidities. One month later, she presented again with symptomatic hypercalcemia. Her Ca was 16.1 md/dL and PTH 761.5 pg/mL. Initial medical management was followed by subtotal parathyroidectomy – three masses were removed (one on the right and two on the left). Final pathology revealed PC within the left parathyroid, the others were consistent with hypercellular parathyroid tissue. One month later, the patient underwent left hemithyroidectomy, right parathyroidectomy, and central neck dissection. PTH level dropped to 2.4 pg/mL and Ca level was 7.6 mg/dL after surgery. She was discharged home on Ca and vitamin D supplements. Pathology was sent to a referral cancer center and revealed PC vs. atypical PA within the right parathyroid. Discussion: PC is a rare endocrine malignancy. Further, there are not many cases of synchronous PC and PA or multifocal PC. Diagnosing PC preoperatively is challenging since it shares overlapping characteristics with PA. Patients with malignancy commonly present with larger tumor size, higher level of Ca (>14.6 mg/dL), and PTH (5-fold higher than the upper limit of normal). Our patient had a history of multiple admissions due to symptomatic HC. She had no palpable neck masses on exam. Her initial FNA was consistent with PA. Hence, we presumed that her hypercalcemia was caused by PA. Establishing a definitive diagnosis of PC by frozen sections intraoperatively is difficult. Histopathologic findings of atypical cells, high mitotic rate, and cellular invasions can suggest the diagnosis, though they are often negative. Even postoperatively, pathologists often disagree on cytologic interpretation. However, differentiating PA and PC is important since earlier and more aggressive treatment is needed to reduce the morbidity and mortality in case of malignancy.