Autoimmune Hyperthyroidism Occurring Late After Radioiodine Treatment for Volume Reduction of Large Multinodular Goiters

131I treatment is an effective alternative to surgery in patients with a large, (non-)toxic, compressive goiter. Late development of hyperthyroidism after 131I therapy for nontoxic nodular goiter is considered rare. We have seen this complication in 3 of approximately 80 patients treated with radioiodine for volume reduction of a large, multinodular goiter. Three women, aged 60 to 71 years, had large, multinodular goiters causing tracheal compression. They were clinically euthyroid before 131I therapy and had normal free thyroxine (FT4) levels. Serum thyroid-stimulating hormone (TSH) levels were normal in 2 patients and undetectable in 1 patient. Patients 1 and 2 received a single dose of 86 and 48 mCi 131I, respectively. Patient 3 received 20 mCi 131I twice (interval 1 month). Clinical and biochemical thyrotoxicosis with high thyroid radioactive iodide uptake (RAIU) developed 10, 6, and 3 months after 131I therapy, respectively, although at control visits 1 to 3 months earlier, serum TSH and FT4 levels were normal. Thyrotoxicosis responded well to methimazole in all three patients. The late occurrence of thyrotoxicosis, high RAIU, and good response to methimazole argue against thyroiditis as the cause of thyrotoxicosis. Serum levels of TSH receptor antibodies, which were undetectable before therapy (patients 1 and 2), were clearly elevated in all three patients during thyrotoxicosis. This is in favor of autoimmune hyperthyroidism as the cause of thyrotoxicosis. These cases illustrate that severe autoimmune hyperthyroidism may occur several months after radioiodine treatment for nontoxic, multinodular goiter. Information about symptoms of hyperthyroidism and regular control visits in the first year after therapy are important in these patients.