Parathyroid carcinoma is an uncommon cause of PTH-mediated hypercalcaemia, accounting for 0.55% of patients with primary hyperparathyroidism. We describe a case of parathyroid carcinoma where the usual pre-operative features of this condition were absent, and hence diagnosed on histopathology.
A 72-year-old woman was referred to endocrinology with incidentally noted hypercalcaemia. Past medical history included hypothyroidism and essential hypertension. Family history was unremarkable. Clinical examination including neck was normal.
Relevant investigations: Serum adjusted calcium 2.82 (2.102.60 mmol/l), Alkaline phosphatase 109 (25140 μ/l), PTH 17.6 (1.57.6 pmol/l), Vitamin D 19.8 (>60 nmol/l), Renal Ultrasound and DEXA scans were normal. Other causes of hypercalcaemia were excluded. She was started on Vitamin D capsules; subsequent calcium levels were 2.822.87mmol/l, with one off reading of 3.01.
Neck USS revealed 1.5 cm adenoma in the left superior parathyroid area and Sestamibi scan confirmed this. On patients choice, parathyroidectomy was performed with complete excision of the tumour weighing 900 mg and measuring 17 mm in size. Histology revealed an enlarged parathyroid with a thick capsule, showing areas of incipient capsular invasion and intra-capsular vascular invasion, compatible with a parathyroid carcinoma.
Post operatively she remained well and normocalcaemic. At the regional MDT meeting, no further treatment was advised as the tumour was completely removed. Repeat ultrasound of neck was normal at 6 months.
Pre-operative features more suggestive of a diagnosis of parathyroid carcinoma young age, palpable neck mass, recurrent laryngeal nerve palsy, extremely high calcium (above 3.5 mmol/l) and PTH levels (310 times above the upper limit), renal and skeletal disease, were all absent.
This case highlights the importance of considering parathyroid carcinoma as a differential diagnosis in PTH-mediated hypercalcaemia, despite being rare, and the lack of typical features.