Evaluation of Indium-111 Pentetreotide Somatostatin Receptor Scintigraphy to Detect Recurrent Thyroid Carcinoma in Patients with Negative Radioiodine Scintigraphy

The follow-up of patients who underwent thyroidectomy for differentiated thyroid carcinoma is based on the combination of serum thyroglobulin (Tg) measurement and radioiodine total-body scan (ITBS). The diagnostic strategy to be used in patients with elevated serum Tg level but negative ITBS remains debatable. Somatostatin receptor scintigraphy (SRS) has been proposed. Our objective was to compare the results of SRS and conventional radiological imaging (CRI) for the diagnosis of recurrent disease and/or metastases in 15 patients who had had thyroidectomy for differentiated carcinoma (14 papillary, 1 Hürthle cell carcinoma) and who displayed elevated Tg levels (10 to 65000 ng/mL) together with negative ITBS performed after 100 mCi. All patients underwent SRS and CRI within 3 months, allowing comparison of the 2 approaches for the identification of thyroid carcinoma metastases. CRI first included a chest x-ray and ultrasonography of the neck. It was followed by computed tomography (CT) scanning and/or magnetic resonance imaging (MRI) of the neck, chest and occasionally abdomen, and ^99mTc bone scintigraphy in case of negative results. In 6 patients with Tg levels ranging from 65 to 65000 ng/mL, CRI detected 12 histologically proven metastases among 9 organs. Among these patients, SRS identified only 6 metastases. SRS identified 1 case of mediastinal recurrence that was not detected by CRI. In another patient with a Tg level of 51 ng/mL, a cervical node was identified using both SRS and CRI but proved to be a false-positive (inflammatory cervical node). In the other 8 patients with Tg levels ranging from 10 to 580 ng/mL, SRS and CRI were negative, and the source of Tg secretion remains unknown. The results of SRS did not correlate with serum Tg level. In conclusion, the diagnostic accuracy of SRS in this study was disappointing and clearly lower than that of CRI. Our results do not support the use of SRS as a guide conventional imaging modalities in patients operated on for differentiated thyroid carcinoma who display elevated Tg levels together with negative ITBS.