Determination of medullary thyroid carcinoma metastases by 201Tl, 99Tcm(V)DMSA, 99Tcm-MIBI and 99Tcm-tetrofosmin.

Medullary carcinoma of the thyroid (MCT) is malignancy derived from the parafollicular cells (or C-cells) of the thyroid. It is usually sporadic, although it is familial in some cases. Several scintigraphic procedures can provide information regarding the primary and metastatic foci of the tumour. We performed whole-body scanning to establish the pathology of MCT using 201Tl, 99Tcm(V)DMSA and 99Tcm-MIBI in 14 patients, and found average sensitivities of 73%, 82% and 81%, respectively. Moreover, we also scanned three patients with 99Tcm-tetrofosmin and identified two of four pathological foci as well as residual thyroid tissue. The sensitivities of 201Tl, 99Tcm(V)DMSA and 99Tcm-MIBI were 100%, 100% and 85% in identifying lymphadenopathies; 40%, 50% and 71% for soft tissue foci; 100% and 100% for foci in pulmonary parenchyma; and 100%, 66% and 100% for recurrences in thyroid gland. Although 99Tcm(V)DMSA identified all bony metastases in three patients (100%), 99Tcm-MIBI detected only two of three foci (66%) and 201Tl none. 201Tl, 99Tcm-MIBI and 99Tcm-tetrofosmin accumulated in residual thyroid tissue, but 99Tcm(V)DMSA did not, as expected. We conclude that these agents were complementary, since they had different sensitivities in different tissues. The tumour-seeking properties of tetrofosmin are to be evaluated in a larger series.