Context: Parathyroid carcinoma is a very rare malignancy. It arises as a separate structure rather than from a pre-existing parathyroid adenoma. It may be difficult to differentiate it from parathyroid adenoma based on histology. When evaluating primary hyperparathyroidism clinical correlation should be taken into account. Clinical features of parathyroid carcinoma may include male gender, palpable neck nodule and higher parathyroid hormone and serum calcium levels associated with symptoms of hypercalcaemia.
Case description: A 67-year-old gentleman was diagnosed with primary hyperparathyroidism in 2007. He had raised adjusted calcium and PTH on routine blood test. An ultrasound of the neck did not identify any parathyroid adenoma but a SESTAMIBI scan raised the possibility of one. He had neck exploration surgery with left superior parathyroidectomy in January 2008. Following surgery his adjusted calcium and PTH were back to normal levels. Tissue histology revealed features of parathyroid adenoma with no malignancy. He was discharged from clinic follow-up but his GP was advised to check his serum calcium annually. He re-presented in March 2018 with raised adjusted calcium and PTH. Ultrasound revealed an enlarged parathyroid gland in the lower pole of the left thyroid lobe which was confirmed on SESTAMIBI scan. He went on to have a left inferior parathyroidectomy in August 2018 without resolution of hypercalcaemia. Postoperative histopathology has confirmed parathyroid carcinoma. He then had further surgical interventions including excision of parathyroid glands on both sides of the neck, left thyroid lobectomy and level VI clearance but with persistent hypercalcaemia. He has now been referred for adjuvant radiotherapy.
Conclusion: Histopathology examination may fail to confirm parathyroid malignancy following parathyroidectomy. The presence of some clinical features as mentioned above should raise the alarm bell and warrant regular and longer calcium monitoring post operatively even if the postoperative histopathology examination revealed no evidence of parathyroid carcinoma.