Background: In the management of patients with differentiated thyroid carcinoma, direct comparison of the presence of scintigraphic stunning after a diagnostic dose of 131I with subsequent successful ablation has not been evaluated.
Methods: This study included 245 patients who received a dose of 2775-3700 MBq of 131I for thyroid remnant ablation. In all patients, the thyroid-stimulating hormone (TSH) level before ablation was more than 30 microlU x ml. One hundred and twenty-six patients (Group A) were given a 185 MBq diagnostic scan (Dscan) 4-11 days before 131I ablation, and 119 patients (Group B) received 131I ablation directly after thyroidectomy. Scintigraphic stunning was considered to be present on any post-ablation scan that revealed either fewer foci or obviously less prominent uptake compared with the earlier corresponding Dscan. Successful ablation was defined as no visible uptake in the neck region or anywhere else on a follow-up Dscan 6-12 months later.
Results: Our results revealed that only 13 of the 126 patients (10.3%) in Group A had visually apparent thyroid stunning. Successful ablation was obtained in 56 of 126 cases (44.4%) in Group A, compared with 86 of 119 cases (72.2%) in Group B (P<0.001). In Group A, the success rate of ablation in patients with stunning (5/13) was not statistically different from that in those without (51/113) (odds ratio, 0.76; 95% CI, 0.23-2.47). Multiple logistic regression analysis revealed that the independent determinants of successful ablation were the use of Dscan before ablation (odds ratio, 0.23; 95% CI, 0.10-0.56) and the ablation dose of 131I (odds ratio, 1.05; 95% CI, 1.00-1.10).
Conclusions: Visually apparent stunning is infrequent and may not be sufficiently sensitive to detect the influence of a 185 MBq Dscan on subsequent ablation outcome. For patients with differentiated thyroid carcinoma, we recommend that ablation should be performed directly after thyroidectomy.