Graves’ disease: is hyperthyroidism still present 6 months after radioactive iodine treatment really a failure?
Merve Nur Acar Tayyar, Ercan Uyanik, Mehmet Mülazimoğlu, Müge Öner Tamam, Savaş Karyağar, Meryem Eslem Biçen Altin, Fatma Zehra Yildiz Kabaca, Merve Cinoğlu KaracaAim
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.
Method
A total of 104 patients diagnosed with Graves’ disease who either developed hypothyroidism or remained euthyroid within 24 months of receiving a single dose of RAI treatment, and who were regularly followed up for at least 2 years, were analyzed retrospectively. All patients had undergone iodine uptake testing and showed no evidence of extrathyroidal symptoms or thyroid nodules on ultrasound scans performed before treatment. The study population was divided into two groups: those who developed hypothyroidism within 6 months, and those who developed it after 6 months. The relationship between the timing of hypothyroidism onset and various factors, including age, gender, RAI dose, 2- and 24-h iodine intake values, post-RAI thyroid-stimulating hormone (TSH) levels, and the need for antithyroid drugs (ATDs) after RAI, was evaluated. Statistical analysis was performed using SPSS for Windows, version 25.0, with a
Results
The mean age of the 104 (74 females and 30 males) patients included in our study was 46.7 ± 13.0 years. The mean administered dose of RAI was 10.6 ± 4.4 mCi, and the average duration of hypothyroidism was 5.5 ± 5.4 months. Among the patients, 15 were euthyroid and 89 were hypothyroid. Hypothyroidism developed within the first 6 months in 65 patients, and after 6 months in 24 patients. In patients with late-onset hypothyroidism (>6 months), the 2-h iodine uptake values were significantly higher, and post-RAI TSH levels were significantly lower. While 58.5% of patients with early-onset hypothyroidism (<6 months) required 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. In both univariate and multivariate Cox regression analyses, the need for ATD therapy after RAI was identified as an independent predictive factor for late-onset hypothyroidism. 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. In addition, 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 sixth 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.