The effect of changes of serum thyrotropin receptor antibody on the outcome of radioactive iodide therapy for Graves' hyperthyroidism

45 Objectives: Serum levels of serum thyrotropin receptor antibody (TRAb) changes widely within 1 year after radioactive iodine therapy (RAI) for Graves’ hyperthyroidism (GH) We investigated the influence of changes in TRAb on outcome of single RAI for GH. Methods: Ninety-eight patients (Male/Female 29/69. median age 44yrs.) with GH who were to undergo first RAI were enrolled. TRAb (normal range: < 2.0 IU/L) was determines by ECLIA method. TRAb values before RAI (TRAb-pre) ranged from 1.3-40.0 (median 13.9). Thyroid weight (TW: g) was determined using either CT or US. TW before RAI ranged from 11 to 195(median 48). Seventy-nine patients, who had been pretreated by anti-thyroid drugs (ATD), discontinued ATDs 3 to 4 days prior to RAI. Patients followed a low iodine diet (< 200μg/day) from 7 days before to 3 days after RAI. The dose of I-131 was individually determinedly to deliver more than 100 Gy to the thyroid gland except for 11 patients in whom thyroid weight exceeded 100g. Thyroid function (FT3, FT4, TSH), TRAb, and thyroid weight was determined at 6, 12, 24, 36, 48, and 60 mos. after RAI. All patients were followed up for more than 5 years without additional RAI. Success of RAI was defined as achievement of either of euthyroid, subclinical hypothyroid, or hypothyroid status. Relationship among changes in TRAb, outcome of RAI, and changes in thyroid weight were evaluated. Results: The average value of TRAb at 6(TRAb-6) 12(TRAb-12), 24(TRAb-24), 36(TRAb-36), 48(TRAb-48), and 60 moths (TRAb-60) was 391%(p 125% of TRAb-6) in 69% (31/45), 53% (24/45),43% 37% (17/45), 24% (11/45), and 11% (5/44) of the patients. The average value of TW at 6 (TW-6), 12(TW-12), 24(TW-24), 36(TW-36), 48(TW-48), and 60 months (TW-60) after RAI was 37%(p<0.01), 20%(p<0.005), 14%(p<0.001), 12%(p<0.001),11%(p<0.001), and 9% (p<0.001) of that of TW-pre, respectively. TW-6 and TW-12 in group A were higher than those in group B and group C (p<0.05 and p<0.05), while there was no significant difference in TW-24, TW-36, TW-48, and TW-60 among 3 groups. Successful rate of RAI at 7(SR-6), 12(SR-12). 24(SR-24), 36(SR-36). 48(SR-48), and 60(SR-60) was 64% (65/98), 80% (78/98), 83(81/98), 88% (86/98). 90% (88/98) and 91% (89/98), respectively. SR-6 and SR-12 in group A vs. group B vs. group C were 60% vs .64% vs. 80% and 76% vs. 86% vs. 88%, respectively. SR-6 and Sr-12 in group A were significantly lower in group A compared with group C (p<0.05 and p<0.05). There was no significant difference in SR- 24, SR-36, Sr-48 and Se-60 among 3 groups. However, recurrence of hyperthyroidism was observed in 3 patients in group A who showed persistent high TRAb. Conclusions: Elevation of TRAb at 6 months after RAI was observed in more than 40% of patients who underwent RAI for GH. Temporary increase in TRAb may link with heavier thyroid weight and lower successful rate of RAI during the first year. From second year on RAI, TRAb declined subsequently in conjunction with atrophic change of the thyroid gland. However, persistent high TRAb after RAI may increase the risk pf recurrence of hyperthyroidism.