Thyroid Cancer Detection with Dual-isotope Parathyroid Scintigraphy in Primary Hyperparathyroidism

Thyroid cancer cells have been shown to take up Tc-99m-sestamibi. The role for Tc-99m-sestamibi scintigraphy (Tc-MIBI) in the diagnosis of thyroid cancer in patients with primary hyperparathyroidism (PHPT) is unclear. Our aim was to determine whether dual-isotope parathyroid scintigraphy is useful in identifying thyroid cancer. A prospective database of 3,187 patients who underwent neck exploration for PHPT was reviewed to identify patients who had concurrent thyroid resection. Patients with benign and malignant thyroid disease were comparatively analyzed. A total of 470 patients underwent both thyroidectomy and parathyroidectomy (reoperations in 21%). Benign disease (n = 391, 83%) was more common than malignancy [papillary thyroid cancer (n = 75) and medullary thyroid cancer (n = 5); 1 had both]. Dual-isotope scintigraphy obtained in 374 patients (80%) had a sensitivity of 67% and a positive predictive value of 66% for parathyroid adenoma localization in these patients with thyroid disease. False-positive scintigraphy occurred in 22% with benign and 45% with malignant thyroid disease (P = 0.002). On Tc-MIBI imaging, 54 (86%) of 63 patients with malignancy had hot nodules, compared to 248 (81%) of 308 patients with benign disease (P = 0.49). On I-123 imaging, 34 (54%) of 63 patients with malignancy had cold nodules, compared to 42 (14%) of 304 patients with benign disease (P < 0.001). A dual-isotype phenotype of both Tc-MIBI-Hot and I-123-Cold had sensitivity 52%, specificity 88%, positive predictive value 47%, and negative predictive value 90% for detecting a thyroid malignancy. A Tc-MIBI-Hot/I-123-Cold phenotype is very specific for detecting thyroid malignancy. Patients with this imaging phenotype should strongly be considered for preoperative ultrasound-guided biopsy. Patients found intraoperatively to have false-positive parathyroid scintigraphy should be evaluated for thyroid cancer.