Localization of Metastatic Parathyroid Carcinoma by18F FDG PET Scanning

Abstract

A 47-yr-old man, diagnosed with parathyroid carcinoma in1989(1),wasnotedonroutine follow-up18yr later to have raised adjusted calcium (2.82 mmol/liter) and PTH (29.9 pmol/liter; normal range, 1.3–6.8 pmol/liter) after previously normal values. Serum calcium continued to increase despite treatment with a calcimimetic (Cinacalcet) at a dose of 60 mg twice daily for 1 month, and the patient required iv pamidronate to reduce his calcium level. The patient was otherwise well, with normal clinical examination and neck ultrasound. Thoracic computed tomography (CT) demonstrated a 1 1.5-cm nodule in the right lung of unknown significance, not amenable to percutaneous biopsy. Technetium 99m-sestamibi examination and indium-labeled octreotide whole body and single photon emission CT of the mediastinum were normal (Fig. 1). Subsequently, an Ffluorodeoxyglucose positron emission tomography (FFDG PET) CT was performed, which showed increased F-FDG activity with a maximum standardized uptake value (SUV max) of 3.2 in the lung nodule. The nodule was removed by open thoracotomy with immediate and sustained normalization of the serum calcium (postoperative PTH,6.1pmol/liter; adjustedcalcium,2.04mmol/liter).Calcium remains normal 12 months after surgery. Histology demonstrated metastatic parathyroid carcinoma. Parathyroid carcinoma is an uncommon cause of hyperparathyroidism, forming less than 1% of all cases of primary hyperparathyroidism (2, 3). Metastases may occur many years after original diagnosis, and the most common sites are: lung (40%), cervical lymph nodes (30%), and liver (10%) (3). Technetium 99m-sestamibi has a sensitivity of 79% (4) in detecting metastases preoperatively. No single imaging modality successfully locates all metastatic sites, and a multimodality approach is essential in these patients. F-FDG PETCTcanbeuseful inpatientswithparathyroidcarcinoma in addition to its use in parathyroid adenomas (5). Distant metastases are common in parathyroid carcinoma, and in patients with abnormal biochemistry all imaging modalities available, including F-FDG PET CT, should be employed to detect the site.