Postsurgical thyroid remnant ablation with radioiodine (131I) is a key element in treatment for selected differentiated epithelial thyroid cancer (DTC) patients. This procedure requires TSH activation of tissue, which is traditionally achieved by withholding thyroid replacement therapy to induce an endogenous TSH rise. However this causes clinical hypothyroidism with unpleasant symptoms. An alternative approach is the use of recombinant human TSH (rhTSH) in the euthyroid state.

In a previous prospective randomised trial, researchers demonstrated comparable successful postsurgical 131I thyroid remnant ablation rates in two groups of low-risk DTC patients who were prepared with either endogenous TSH stimulation induced by 4 or more weeks of thyroid hormone withdrawal or by rhTSH. Successful ablation was defined as either no visible uptake or > 0.1% thyroid bed uptake of the administered 131I activity on imaging 8 months after therapy. Based on the secondary criteria of no visible uptake alone or a stimulated serum thyroglobulin (Tg) level < 2 ng/ml at 8 months, there were no significant differences between the hypothyroid and euthyroid patient groups.

In the current study, most patients from the original groups were re-examined ≥ 3 years later to determine whether current TSH-stimulated testing confirmed that the comparability of thyroid remnant ablation success had persisted and whether there has been any difference in patients’ clinical outcomes.

Of the 63 original patients, 51 (28 euthyroid, 23 hypothyroid) participated in this present study, and 48 received rhTSH and serum thyroglobulin (Tg) sampling. A 131I whole-body scan was performed in 43 patients, and successful ablation was defined by criteria from the previous study. The following findings were reported:

• Based on the criterion of uptake < 0.1% in thyroid bed, 100% (43 of 43) remained ablated.

• When the criterion of no visible uptake was used, 5 patients (4 euthyroid, 1 hypothyroid) had minimal visible activity.

• When the TSH-stimulated Tg criterion was used, 2 of 45 (1 euthyroid, 1 hypothyroid) had a stimulated Tg level > 2 ng/ml.

• No patient in either group died, and no patient declared disease free had sustained tumour recurrence.

• 9 (4 euthyroid, 5 hypothyroid) had received additional 131I between the original and current studies due to evidence of disease; with follow-up, all now had a negative rhTSH-stimulated whole-body scan and 7 (3 euthyroid, 4 hypothyroid) had a stimulated serum Tg < 2 ng/ml.

The authors conclude “the current study performed a median 3.7 yr after postsurgical 131I thyroid remnant ablation found no differences in the success of thyroid remnant ablative radioiodine therapy or clinical outcomes between patients prepared by endogenous TSH stimulation by withholding thyroid hormone therapy vs. exogenous rhTSH in the euthyroid state. There were no differences between the two approaches in eliminating thyroid remnants or in instances of residual disease detected. These findings confirm that rhTSH is an effective and safe alternative to thyroid hormone withdrawal in preparing low-risk DTC patients for the postsurgical thyroid remnant ablation.”