Clinical approach in patients with metastatic differentiated thyroid carcinoma and negative 131I whole body scintigraphy: importance of 99mTc MIBI scan combined with high resolution neck ultrasonography.

AIMS AND BACKGROUND: The aim of this study was to define the clinical impact of MIBI scan combined with neck ultrasonography on the detection of metastates in differentiated thyroid carcinoma (DTC) patients with elevated serum Tg levels but negative 131I scan (non-functioning DTC). METHODS AND STUDY DESIGN: Eighty-two patients with non-functioning DTC, 19 patients with 131I-positive metastases (functioning DTC), and 24 DTC patients who were disease free after therapy (no cancer patients) were enrolled. 131I scan was performed after administration of low diagnostic and high therapeutic tracer doses. Early and delayed images were obtained after MIBI injection. Neck-chest CT scan and/or MRI were also performed in patients with non-functioning DTC. RESULTS: In the group of non-functioning DTC patients, metastatic foci were detected in 71/82 cases: in the cervical lymph nodes in 51 cases (sensitivity 94.1% with MIBI, 90.2% with US, 35.3% with CT/MRI), mediastinal lymph nodes in 31 cases (sensitivity 100% with MIBI, 58% with CT/MRI), lungs in 8 cases (sensitivity 100% with both MIBI and CT/MRI), and bone in 2 cases (sensitivity 50% with MIBI, 100% with MDP bone scan). Among the 19 patients with functioning DTC a close relationship between MIBI and 131I findings was observed. As regards the 24 tumor-free patients, MIBI was correctly negative in all cases, while US visualized enlarged cervical lymph nodes that were suspected to be neoplastic but proved to be inflammatory lesions at cytology in three patients. CONCLUSIONS: On the basis of these data, MIBI scan combined with neck US could be proposed as a first-line diagnostic imaging modality in the follow-up of DTC patients with elevated serum Tg levels and negative 131I scan.