Atypical parathyroid tumour is a rare cause of primary hyperparathyroidism. We present a case of atypical parathyroid tumour, presenting with multi-glandular primary hyperparathyroidism.

A 40-year-old Asian female patient with polyuria and polydipsia was admitted for hypercalcemia. She had no family history of hypercalcemia or primary hyperparathyroidism. On physical examination, there was no palpable neck mass. Her serum adjusted calcium was 3.04 mmol/L (2.1-2.65), phosphate 0.62 mmol/L (0.8-1.5), PTH 103 pmol/L (1.6 to 7.2). Total vitamin D level was 19 nmol/L. Creatinine was normal, 24 hour urine calcium 11.65 mmol/day (<6.25), ultrasound kidney no stones. She was osteoporotic, lowest T score -3.2 at the distal radius. Ultrasound neck localised a 1.4cm hypoechoic solid lesion posterior to the left upper pole of thyroid. Sestamibi SPET/CT revealed a markedly MIBI avid soft tissue nodule at right upper paratracheal region posteroinferior to right lower pole of thyroid, measuring 1.4x2.2x3.9cm. Another mildly MIBI avid soft tissue nodule posterior to left upper pole of thyroid corresponding to USG thyroid findings.

Bilateral open parathyroidectomy was performed. A 3cm right lower parathyroid adenoma and 2cm left upper parathyroid adenoma was excised. Intraop PTH dropped from 150 to 133 pmol/L. PTH remained elevated >100pmol/L during subsequent follow up. 4D CT neck was arranged, showing a 3.3cm solitary parathyroid adenoma at the right thoracic inlet, just at the level of the right sternoclavicular joint (Figure 1). Right lower parathyroidectomy was done, resecting a 3x2x1.5cm parathyroid adenoma at the right paratracheal grove. Intraop PTH dropped from 149 to 13 pmol/L, PTH ratio 91.3%. Pathology revealed occasional tumour cells possessing irregularly enlarged hyperchromatic to vescicular nuclei with coarse chromatin. The tumour-capsular interface was irregular. Ki67 index was 3.2%. In view of atypical cytological and architectural features but lack of unequivocal evidence for parathyroid carcinoma, features were most consistent with atypical parathyroid tumour. CDC73 gene mutation test came back negative. Calcium, PTH and ultrasound neck showed no recurrence 3 years after surgery.

Atypical parathyroid tumours have uncertain malignant potential. Most cases do not recur after complete excision but metastases have been reported. Serum calcium, PTH and neck ultrasound should be monitored post-operatively. Germline CDC73 mutations have been identified in association with these tumours and should also be performed.