Follow-up of differentiated thyroid cancer: comparison of multiple diagnostic tests

The radioablation of thyroid remnants improves the prognosis of differentiated thyroid cancer. In our prospective study an activity of 3.7 GBq 131I failed to completely ablate the remnants in 46 out of 101 patients, but a 3-year follow-up period was uneventful. One other patient had a recurrence early after thyroidectomy. In view of possible stunning effects of 131I it might be advantageous to visualize such remnants by imaging modalities which do not emit beta-particles. Our data have revealed that neither magnetic resonance imaging (MRI), nor ultrasonography (US), nor 99Tcm-sestamibi scintigraphy, nor positron emission tomography could detect or reliably exclude minimal remnants. Such remnants did not produce thyroglobulin (Tg). A 123I and 131I uptake of> 10% after thyroidectomy was associated with about a 90% probability of persistent remnants. On the other hand, MRI was helpful in the patient group (n = 32) with Tg>4ng x ml(-1) at the second whole-body scintigraphy (TSH>30 mU x l(-1)) for planning the management of lymph node metastases (n = 15 patients): 12 patients had subsequent surgery and three patients radioiodine therapy. We recommend that MRI be used early in follow-up care when Tg is elevated. The decision of whether or not to treat persistent thyroid remnants should not be made on the basis of MRI, US or nonspecific scintigraphic methods. Complete ablation did not appear to have any clinical benefit in our study group.