Abstract
Thyroid stunning is discussed mainly regarding thyroid carcinoma patients undergoing radioiodine treatment. Attempts have been made to identify the highest absorbed dose that does not cause stunning. Previously, we showed that stunning was evident in primary cultured porcine thyrocytes exposed to 0.15 Gy from 131I. If this result is applicable in vivo, stunning would be found also in hyperthyroid patients receiving 131I therapy, since the absorbed dose from the diagnostic amount of 131I is typically 0.1-0.3 Gy.
The aim was to investigate whether thyroid stunning could be identified in patients receiving radioiodine treatment for benign thyroid disease. We measured 131I uptake in nineteen patients diagnosed with Graves disease or toxic nodular goiter at one and six days after administration of diagnostic (0.45-0.62 MBq) and therapeutic (200-620 MBq) amounts of 131I. The estimated effective half-life, the absorbed dose delivered per unit activity administered, and serum antibodies against thyroperoxidase, TPO-Ab, and TSH receptor were evaluated. 131I uptake after therapy as compared to after diagnostics varied widely among individual patients. In 26% (day 1) and 47% (day 6) of patients, therapeutic uptake was lower than diagnostic uptake, suggesting stunning. There was a significant correlation between the absorbed dose from diagnostic 131I and the change in estimated effective half-life from diagnostics to therapy and the change in absorbed dose per unit activity at therapy versus diagnostics. No overall changes in effective half-life or uptake for diagnostic or therapeutic 131I were detected. The significant negative correlations between absorbed dose from diagnostic 131I and the change in estimated effective half-life, and the absorbed dose delivered per unit activity, suggest thyroid stunning. Further studies are needed to establish a connection between absorbed dose, time, and stunning, for low absorbed doses of 131I.