Graves' disease: is hyperthyroidism still present 6 months after radioactive iodine treatment really a failure?

Aim: This study aimed to evaluate the accuracy of the 6-month evaluation to accept treatment failure after a single dose of radioactive iodine (RAI) for Graves' disease and to decide whether to repeat the dose.

Methods: This study retrospectively analyzed 104 patients who received a single dose of RAI between 2003 and 2022, had regular follow-up for at least 2 years, and did not have extrathyroidal symptoms. The study group was divided into two groups: patients who developed hypothyroidism within the first 6 months and patients who developed hypothyroidism after 6 months, and statistically analyzed.

Results: The mean administered dose of RAI was 10.6 ± 4.4 mCi, and the average duration of hypothyroidism was 5.5 ± 5.4 months. In patients with late-onset hypothyroidism (>6 months), the 2-h iodine uptake values were significantly higher, and post-RAI thyroid-stimulating hormone levels were significantly lower. While 58.5% of patients with early-onset hypothyroidism (<6 months) required antithyroid drug (ATD) therapy after RAI, all patients who developed hypothyroidism after 6 months received supportive ATD treatment. The 24-h iodine uptake values were significantly higher in the hypothyroid group compared with the euthyroid group. During follow-up, 26.9% of patients were hypothyroid at 0-3 months, 62.5% at 3-6 months, and 77.9% at 12 months. While 20.2% of patients remained hyperthyroid at 6 months, this rate declined to 3.8% at 12 months.

Conclusion: This study suggests that the 6 th month following RAI treatment in patients with Graves' disease may not be sufficient to assess treatment response, as hypothyroidism tends to develop cumulatively over time. Iodine uptake values at 2 and 24 h may serve as useful indicators for predicting the development of early or late hypothyroidism, while also helping to guide the maintenance of a euthyroid state.