Endocrine Abstracts

Parathyroid carcinoma (PC) rarely presents with metastasis at diagnosis and usually in patients also having gross local invasion.

Case presentation: We report the case of a 51-year-old postmenopausal woman presenting at our institution in June 2019 with symptomatic hypercalcemia (fatigue, polyuria, constipation and bone pain), but with a surprisingly good general condition. She had been treated with bisphosphonates for osteoporosis (DXA: LS T score −4.2 S.D., Z score −3.6 S.D.; FN T score −2.4 S.D., Z score −1.7 S.D.) for 2 years, having a variable hypercalcemia up to 12.6 mg/dl, but undiagnosed for primary hyperparathyroidism (PHPT). She had no family history of parathyroid disease or endocrine neoplasia. Initial laboratory findings revealed marked hypercalcemia (17.5 mg/dl), very high PTH levels (1561 pg/ml) and turnover (CTX 4.58 ng/ml) and normal kidney function, which led to the suspicion of PC. Neck ultrasound showed a hypoechoic tumor with slightly irregular margins, Ø max 1.5 cm, in the position of right superior parathyroid gland. The tumor was surgically removed and three other parathyroids were identified in canonical location and of normal appearance, with no gross invasion. As the preliminary pathology report revealed characteristic features of PC, a total thyroidectomy was performed, and a small normal parathyroid gland was found adjacent to the initial tumor. After tumor removal, her PTH levels decreased by 65%, from 1561 pg/ml to 560 pg/ml (Ca 11.34 mg/dl) and then increased fast, at the the same rate as preoperatively: 39% in 3 weeks preop vs 39% in 1 mo postop; and progressively reached 1684 pg/ml after 3 mo. A MIBI scan including the mediastinum was negative and a FDG−PET CT showed increased metabolic activity in a 10 mm nodule, in the right para aortic mediastinal pleura, the descending colon and skeleton. A bone scan showed homogenous symmetrical uptake throughout the skeleton and X-rays were normal. A CT scan confirmed a mediastinal nodule measuring 11/7/13 mm, tangent to the right antero-lateral face of the ascending aorta and bilateral pulmonary micronodules. Total serum Ca was variably controlled (9.1 mg/dl to 15 mg/dl) with pamidronate and then denosumab (60−120 mg). The surgery performed abroad confirmed that the mediastinal nodule was a metastasis of PC. Eventually, the hypercalcemia became resistant to denosumab (6 mo postop) and the patient died due to a hypercalcemic crisis (20 mg/dl).

Conclusion: This is a rare case of a small and very aggressive parathyroid carcinoma with lung metastasis at diagnosis although with no local invasion.