Case Presentation: A 42-year-old Ethiopian woman presented to the emergency department complaining of an enlarging neck mass, dysphagia, anorexia, vomiting and constipation for the previous two weeks. She had no relevant past medical or family history. On admission, she became acutely altered requiring intubation for airway protection. She was normotensive and tachycardic, and a significant firm, non-tender right-sided neck mass was evident on exam. Laboratory results showed a serum calcium of 25.2mg/dL, ionized calcium > 3.0mmol/L, parathyroid hormone (PTH) level >1900pg/mL, undetectable vitamin D level and elevated creatinine to 1.7mg/dL, consistent with acute hypercalcemic crisis due to PHPT. Initial management included intensive fluid therapy, calcitonin and cinacalcet. Continuous renal replacement therapy was initiated as well due to severity of hypercalcemia and acute renal failure. Her course was complicated with supraventricular tachycardia requiring amiodarone infusion. Thyroid ultrasound and computed tomography revealed a large heterogenous posterior right lobe mass, however no other masses were identified on imaging studies. 99mTc sestamibi report indicated hyperfunctioning lesion inseparable from right thyroid lobe with posterior extension and marked peripheral tracer uptake, suggestive of central necrosis. She subsequently underwent neck exploration with right parathyroidectomy and right hemithyroidectomy. Pathology report of 6.7cm mass confirmed low grade parathyroid carcinoma with local invasion of thyroid lobe and absent metastatic disease to lymph nodes. Five days postoperatively, patient became symptomatically hypocalcemic and required calcium supplementation. She recovered successfully with appropriate normalization of calcium and PTH levels.

Discussion: PHPT secondary to parathyroid tumors must be considered in the differential diagnosis for severe hypercalcemia in all age groups. Parathyroid carcinoma accounts for only 1-3% of cases of PHPT and 0.005% of all cancers, therefore it is one of the rarest malignancies. It is associated with increase mortality when severe acute hypercalcemia is present due to possible cardiac and renal complications, making parathyroid crisis a surgical emergency. Diagnosis can be challenging preoperatively unless patient presents with metastatic disease. However, it should be suspected in a young patient with a palpable neck mass with signs of hyperparathyroidism, renal or skeletal disease and extremely elevated calcium and PTH levels up to 10-times greater than normal. Thus, while early recognition is crucial and medical therapy in an important initial step, an aggressive surgical approach is the most effective treatment and provides the best outcome for the patient.

Conclusions: Parathyroid carcinoma is an extremely uncommon cause of primary hyperparathyroidism (PHPT). It can be associated with parathyroid crisis, which can be potentially catastrophic if diagnosis and surgical intervention are delayed.