O-13 Parathyroid carcinoma - a rare and challenging entity
Authors: Martins João Dinis , Pina Henrique , Féria Rita Palma , Moules Pedro , Miranda Pedro , Gomes Catarina , Guerra Sílvia , Marques Joana , Ferreira Marisa Peralta , Valadas Cristina 
Published: January 2024

Abstract

Background
Parathyroid carcinoma is a rare malignancy, accounting for less than 1% of all cases of primary hyperparathyroidism (HPT). This entity affects both men and women equally and is usually diagnosed in the fourth or fifth decade of life. It can occur sporadically or be associated with genetic syndromes such as hyperparathyroidism-jaw tumor syndrome.
Its clinical presentation can overlap with that of primary HPT, with hypercalcemia that can lead to a range of symptoms, such as fatigue, weakness, bone pain, kidney stones, and gastrointestinal disorders.
Distinguished by its rarity and clinical challenges, this condition requires a high level of suspicion and its initial surgical approach correlates with long-term prognosis.

Clinical Case
This is the case of a male patient, 39 years old, Caucasian, with a previous history of hypertension diagnosed 5 months earlier, deep vein thrombosis (DVT) diagnosed 2 months earlier, and active tobacco use.
Additional study performed after the DVT episode found severe hypercalcemia (14.3 mg/dL, N 8.6-10.0), hypophosphatemia (2.2 mg/dL, N 2.5-4.5), and renal dysfunction (Creatinine 1.43 mg/dL). The patient was asymptomatic and was admitted to the Internal Medicine department, to correct the hypercalcemia and further investigation.
Increased PTH levels (1555 pg/mL, N 15-65) were found, and a cervical ultrasound revealed, on the left thyroid lobe, a bilobed nodule, mainly solid, hypoechogenic, with irregular margins and macrocalcifications, with 34×22 mm. Full body CT showed osteolytic lesions on several ribs and both iliacs and kidney stones. A bone scintigraphy was also done, showing a diffuse fixation on the axial and appendicular skeleton, compatible with diffuse osteomedullary infiltration.
Due to these findings, the collaboration of the Endocrinology department was requested. Based on the PTH levels and the characteristics of the cervical mass, suspicion arose regarding a potential case of parathyroid carcinoma. Subsequently, a parathyroid scintigraphy using Sestamibi was conducted, whose report revealed an intense hyperfixation at a nodular formation projecting on the lower two-thirds of the thyroid left lobe, without unequivocal identification of its origin - thyroid nodule vs. parathyroid tissue.
Based on intraoperative findings and clinical suspicion, en bloc resection of the tumor along with the thyroid lobe and unilateral neck exploration was performed by the Surgery department, with the pathological assessment confirming the malignancy diagnosis. The patient was referred to an oncologic tertiary center, for follow-up and genetic testing.

Conclusion
We want to shed light on this rare entity and the importance of multidisciplinary critical thinking, alongside imaging. Markedly elevated PTH and/or calcium levels on a patient with a cervical mass should arouse suspicion of a parathyroid carcinoma, which must not be biopsied and warrants a more extensive surgery to ensure the best possible prognosis.