Long‐term effects of radioiodine on thyrotrophin receptor antibodies in Graves' disease

SummaryOBJECTIVE Graves' disease is recognized as an organ‐specific autoimmune disorder caused by the presence of TSH receptor antibodies. The long‐term effects of 131I treatment for Graves' disease on TSH receptor antibodies have not previously been studied. We have measured the TSH‐binding Inhibitory immunoglobulin (TBII) Index and thyroid stimulating antibody (TSAb) activity in patients with Graves' disease following treatment with 131I.DESIGN A retrospective study.PATIENTS Two hundred and twenty‐five patients with Graves' disease who were treated with 131I 1–13 years earlier were studied (1 year: 27 patients; 2–5 years: 42 patients; 6–9 years: 79 patients; 10–13 years: 77 patients).MEASUREMENTS The TBII index was measured as the percentage 125I‐TSH bound to pig thyroid membranes and TSAb activity as the amount of cAMP produced by cultured FRTL‐5 cells.RESULTS TBII was detected in 78% of patients prior to 131I administration. Following 131I administration, the Incidence of positive TBII was 85% at the end of the first year decreasing to 40,19 and 17% at 2–5,6–9 and 10–13 years, respectively. The frequency of a positive TSAb was 74% at the end of the first year, and also decreased to 49, 27 and 29% at 2–5, 6–9 and 10–13 years, respectively. At more than 2 years after 131I therapy, the frequencies of hyperthyroidism In TBII and TSAb positive patients were 42% (19/45) and 30% (19/63), respectively, which were significantly higher than those In TBII and TSAb negative patients (8%: 12/153 and 8%:11/131, respectively). The frequency of hyperthyroidism after 131I treatment in patients with negative TBII before treatment (7%: 2/29) was significantly lower than that (29%: 30/102) In patients with positive TBII before treatment.CONCLUSIONS These results indicate that (1) the TBII Index and TSAb activity decreased over a period of more than 2 years after 131I therapy for Graves' disease, and (2) the TBII index before treatment may influence the long‐term outcome of 131I therapy.