AUTOIMMUNE HYPERTHYROIDISM OCCURRING LATE AFTER RADIOIODINE TREATMENTFOR VOLUME REDUCTION OF LARGE MULTINODULAR GOITERS

I-131 treatment is an effective alternative to surgery in patients wit h a large, (non-)toxic, compressive goiter. Late development of hypert hyroidism after I-131 therapy for nontoxic nodular goiter is considere d rare. We have seen this complication in 3 of approximately 80 patien ts treated with radioiodine for volume reduction of a large, multinodu lar goiter. Three women, aged 60 to 71 years, had large, multinodular goiters causing tracheal compression. They were clinically euthyroid b efore I-131 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 I-131, respectively. Patient 3 received 20 mCi I-131 tw ice (interval 1 month). Clinical and biochemical thyrotoxicosis with h igh thyroid radioactive iodide uptake (RAIU) developed 10, 6, and 3 mo nths after I-131 therapy, respectively, although at control visits 1 t o 3 months earlier, serum TSH and FT4 levels were normal. Thyrotoxicos is responded well to methimazole in all three patients. The late occur rence of thyrotoxicosis, high RAIU, and good response to methimazole a rgue against thyroiditis as the cause of thyrotoxicosis. Serum levels of TSH receptor antibodies, which were undetectable before therapy (pa tients 1 and 2), were clearly elevated in all three patients during th yrotoxicosis. This is in favor of autoimmune hyperthyroidism as the ca use of thyrotoxicosis. These cases illustrate that severe autoimmune h yperthyroidism may occur several months after radioiodine treatment fo r nontoxic, multinodular goiter. Information about symptoms of hyperth yroidism and regular control visits in the first year after therapy ar e important in these patients.