Preparation of patients with thyroid cancer for ¹³¹I scintigraphy or therapy by 1-3 weeks of thyroxine discontinuation

To assess whether the patient preparation procedure for ¹³¹I scintigraphy could be streamlined, we evaluated the time course of thyroid-stimulating hormone (TSH) elevation after total thyroidectomy or after discontinuation of thyroxine (T₄) in patients with thyroid cancer. Methods: The clinical records of 284 patients with well-differentiated thyroid cancer were reviewed. All patients had undergone total thyroidectomy. Two groups of patients were evaluated. The immediate postoperative group consisted of 176 patients who were not given thyroid hormone replacement after surgery because of planned postoperative ¹³¹I therapy. The surveillance group consisted of 108 patients in whom T₄ replacement was stopped (without triiodothyronine [T₃] replacement) in preparation for surveillance whole-body ¹³¹I scintigraphy. We recorded the first TSH measurement and number of days after surgery or without thyroid hormone for each patient. Results: In the immediate postoperative group, TSH levels obtained 6-65 d (median, 17 d) after surgery ranged from 18.2 to 194.8 μIU/mL (median, 46.6 μIU/mL). The TSH values exceeded 30 μIU/mL in 89% of patients evaluated at 1-2 wk, in 88% of those evaluated at 2-3 wk, and in 90% of those evaluated after 3 wk. In patients discontinuing T₄ (without T₃ replacement), TSH levels obtained from 6 to 35 d (median, 20 d) later ranged from 23.4 to 214.5 μIU/mL (median, 61.1 μIU/mL). The TSH levels exceeded 30 μIU/mL in 100% of patients evaluated at 1-2 wk, in 89% of those evaluated at 2-3 wk, and in 96% of those evaluated after 3 wk. Conclusion: In most patients with thyroid cancer being prepared for ¹³¹I imaging or therapy, a TSH level exceeding 30 μIU/mL can be achieved by withdrawal of thyroid hormone therapy for 1-3 wk.