Primary hyperparathyroidism (pHPT) is common with 85% due to a sporadic solitary adenoma, 10-15% multiglandular disease, and <1% parathyroid carcinoma. Differentiating carcinoma from benign causes at presentation can be difficult. Brown tumour (osteitis fibrosa cystica) is a rare manifestation of severe hyperparathyroidism with locally invasive lesions resembling primary bone tumours or bony metastases.
An 83 year old man admitted with myocardial infarction was incidentally found to have severe, asymptomatic hypercalcaemia (Ca2+ 3.13mmol/L) and hyperparathyroidism (PTH>100pmol/L). Neck ultrasound and sestamibi failed to localise a parathyroid adenoma. MRI showed bilateral enlarged inferior parathyroid glands (L 7.6x12x17mm, R 16x14x15mm) and a right T3 bony lesion, not evident on bone scan. PSA and myeloma screens were negative.
Left inferior parathyroidectomy, left hemithyroidectomy, and partial resection of the left recurrent laryngeal nerve with the enlarged right parathyroid gland left in situ were performed due to an intraoperative suspicion of parathyroid carcinoma. Histopathology showed some atypical features with no definite malignant features. Immunohistochemistry for parafibromin and PGP9.5 was inconclusive.
Staging CT and FDG PET showed a lytic, hypermetabolic T3 soft tissue bony lesion with local invasion. A right T3 hemilaminectomy was undertaken and histopathological examination indicated a brown turmour. A right parathyroidectomy was then performed and histopathology showed features most consistent with glandular hyperplasia or a parathyroid adenoma. Serum calcium and PTH normalised postoperatively and remained stable.
The presence of the bony lesion with hyperparathyroidism raised the possibility of metastatic parathyroid carcinoma, with a differential diagnosis of primary bone tumour, metastasis with co-existing hyperparathyroidism, or brown tumour. Differentiation of parathyroid carcinoma from other benign tumours may be difficult, due to overlapping clinical, biochemical, imaging and histological features. Regardless, clinical suspicion of parathyroid carcinoma or multigland disease demands that all four parathyroid glands should be thoroughly explored to minimise the risk of recurrence.