Stunning phenomenon after a radioactive iodine-131 diagnostic whole-body scan

Purpose Stunning of thyroid remnants after diagnostic scanning (Dx-WBS) using radioactive iodine-131 (131I) may limit the efficacy of 131I therapy. We aimed to evaluate this assumption in a prospectively designed study. Methods Forty patients who underwent thyroidectomy for differentiated thyroid carcinoma were studied and divided into two identical groups: G1 and G2. In the G1 group, no Dx-WBS was performed and the ablation dose was given directly on the basis of the risk stratification; in the G2 group, Dx-WBS was performed with 185 MBq (5 mCi) of 131I, and ablation was given for a mean number of 11±1.1 days; stunning was found on a semiquantitative basis in all patients. At a mean of 6.5±0.3 months, the ablation success rate (ASR) was evaluated on the basis of Dx-WBS, thyroglobulin levels, and neck sonography. Complete ASR was considered when no 131I uptake could be seen in the neck or elsewhere, thyroglobulin was less than 2 ng/ml, and neck sonography was negative for any disease-related abnormalities. Results G1 and G2 groups were completely identical as no significant differences were found between their different characteristics, including the mean ablative dose. ASR was 81.7 and 78.3% in G1 and G2 groups, respectively (P=0.6). Multivariate Cox regression analysis showed the mean ablation dose to be the most influential factor in ASR (odds ratio 1.045; 95% confidence interval 0.936–1.1189; P=0.01). Conclusion Our data suggest that stunning had no influence on ASR and is not a point of clinical consideration with respect to this aspect.