Parathyroid carcinoma with moderate PTH elevation – clinical case review — ASN Events
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Parathyroid carcinoma with moderate PTH elevation – clinical case review (#446)

Tsui Yue Ong 1 , Tamara Preda 2 , Veronica Preda 1
  1. Endocrinology, Macquarie University Hospital, Macquarie Park, NSW, Australia
  2. Department of Surgery, School of Medicine, , University of Notre Dame Australia (Sydney), Australia , Sydney, NSW, Australia

Background: Parathyroid carcinoma is a rare cause of primary hyperparathyroidism and typically presents with marked hypercalcaemia, elevated parathyroid hormone (PTH), renal or skeletal complications, or a palpable neck mass. Mild biochemical presentations may be difficult to distinguish from benign parathyroid disease before surgery.

Case presentation: 49-year-old man had incidentally detected primary hyperparathyroidism, with corrected calcium of 2.80 mmol/L and peak PTH of 28 pmol/L. 24 hour urinary calcium excretion was elevated at 11.4 mmol/day, while renal function and vitamin D level were normal. He reported mild bone pain but had no nephrolithiasis, renal impairment, fragility fracture, neurocognitive or gastrointestinal symptoms, obstructive symptoms, or palpable neck mass. Localisation studies were concordant. Sestamibi imaging demonstrated an avid lesion at the inferior pole of the right thyroid lobe, ultrasound identified a 28 mm heterogeneous right lower pole nodule, and 4D-CT showed a 26 × 29 mm lesion posterior to the right thyroid lobe with features favouring a parathyroid adenoma. The lesion, weighing 6.12g, was excised without complication and was not adherent to surrounding structures. Postoperative calcium and PTH normalised. Specialist pathology review identified an atypical parathyroid neoplasm with features consistent with parathyroid carcinoma, including cytological atypia, vascular invasion, focal capsular disruption, and Ki-67 index of up to 6%. Parafibromin staining was retained.

Discussion: This case demonstrates that parathyroid carcinoma can present with modest biochemical abnormalities and minimal symptoms, while preoperative imaging may suggest a benign adenoma. Diagnosis depends on expert histopathological assessment integrating invasive features and immunohistochemistry. Retained parafibromin staining does not exclude malignancy. Following multidisciplinary review, close surveillance with serial calcium, PTH, and neck ultrasound was recommended, alongside genetic testing. At five months, the patient remained normocalcaemic with no evidence of recurrence or lymphadenopathy.

Conclusion: Clinicians should maintain diagnostic vigilance for parathyroid carcinoma even when biochemical and clinical findings are mild. 

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