Role of Tc-99m pertechnetate for remnant scintigraphy, post-thyroidectomy, and serum thyroglobulin and antithyroglobulin antibody levels in the patients with differentiated thyroid cancer.

Abstract

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. 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. 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. 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.