Aim: Postoperative scanning may help to identify patients with differentiated thyroid cancer (DTC); however, low dose I-131 can lead to stunning and suboptimal response to ablative therapy. The aim of this retrospective study is to compare postablative I-131 scintigraphy with post-thyroidectomy Tc-99m pertechnetate scintigraphy, serum thyroglobulin (Tg) and antithyroglobulin antibody (TgAb) levels in patients with DTC.
Methods: Patients who had undergone surgical thyroidectomy for DTC were evaluated retrospectively. All patients had undergone Tc-99m pertechnetate and postablative I-131 scans. Serum Tg and TgAb levels were measured in all subjects. Preablative pertechnetate scans of the thyroid bed were viewed blindly and then directly compared with postablative I-131 scans and Tc-99m pertechnetate scintigraphy was compared with serum Tg and TgAb levels.
Results: One hundred and seventy-four patients (146 women, 28 men) with a mean age of 48.7 ± 13.1 (range 12-84) years who had undergone surgical thyroidectomy for DTC were evaluated retrospectively. Of 174 patients, 6 (3%) had negative I-131 and also Tc-99m pertechnetate scintigraphy results. Of the remaining 168 positive I-131 scans, 131 (75%) were positive in at least one site on the pertechnetate scan, 19 (11%) were considered to have equivocal uptake and 18 (11%) were negative. For the per-site analysis, pertechnetate sites were considered to be accurately determined if they showed concordant uptake at sites that correlated precisely with those seen on the postablation I-131 scans. There were a total of 356 positive foci on I-131 scans. Of these, 273 foci (77%) were unequivocally positive on pertechnetate scintigraphy, 41 (11%) showed equivocal uptake and 42 (12%) foci could not be detected. There were statistically significant differences (p < 0.0001) between the negative and positive foci in terms of Tg levels on pertechnetate sites.
Conclusions: A positive pertechnetate scan is, therefore, sufficient to guide progression to I-131 ablation in most patients. Pertechnetate scintigraphy may be of particular benefit if it is considered desirable to avoid use of I-131 in post-thyroidectomy remnant imaging. Tg level is an important parameter in the detection of remnant thyroid tissue in patients with DTC.