Changes in serum TSH receptor antibody values in female patients of child bearing age with Graves’ disease after radioiodine therapy

Objectives: Radioiodine I-131 therapy (RAI) is useful in treating Graves’ hyperthyroidism (GH). TSH receptor antibody values (TRAb ) are decreased by RAI. However, changes in TRAb after RAI could be variable. TRAb after RAI may rise or remain persistently high in subsets of patients, which is a risk factor for fetal or neonatal hyperthyroidism in young adult females who wish to conceive after remission of GH.The aim of this study was to determine changes of TRAb following RAI in female patients with childbearing age.

Methods: We prospectively monitored thyroid function and TRAb before and after RAI in 6s female patients with childbearing age(19-39yrs. Average 32yrs). 61 out of 68 patients had been pretreated by anti-thyroid drugs (ATD: methimazole or propylthiouracil) and/or potassium iodide (KI). ATDs were withdrawn 3 to4 days prior to RAI while KI was withdrawn 14 days prior to RAI. Patients had a counselling with a dietitian and were instructed to follow a low iodine diet from 7 days before to 3 days after administration of I-131.TRAb ( normal range: < 2.0 IU/L was determined using a E-CLEA kit. The median value of TRAb values before RAI was 11.8. Thyroid weight (TW:g) was determined using US or CT.Dose of I-131 was adjusted so that more than 100Gy was delivered to the thyroid except for 7 patients having a large goiter(TW >100g). Otherwise, 555 MBq of I-131 was administered.The median duration of follow up after RAI was 74 months. It was defined as that patients were in remission when either of euthyroidism, subclinical hypothyroidism, or hypothyroidism was achieved, and patients were released from taking ATDs and/or KI.

Results: Remission of hyperthyroidism was observed in 59 out of 68 pts. (89%) with a median duration of 6.3 months (95%CI: 5.4-13.8) after RAI. Of 59 patients, 47 (80%) entered remission within the first year after RAI. The remaining 10 patients required retreatment. Normalization of TRAb(< 2.0) was observed in 42 (71%) among those who entered remission with a median duration of 37.8 mos. (95%CI:18.5-46.0). The achievement rate of normalization of TRAb was significantly lower than that of Remission of GH (p=0.031). In addition, compared with achievement of remission, it took longer period for TRAb to normalize (p=0,013).Eleven patients got pregnant with a median interval of 28 months after RAI. At the diagnosis of pregnancy, TRAb was below than 2.0 in 7, 2.0-10.0 in 2, and higher than 10 in one, respectively. Artificial or spontaneous abortion was not observed. None of eleven newborns were associated with neonatal hyperthyroidism.

Conclusions: Our study shows that normalization of TRAb after RAI for GH requires longer period than that of remission of hyperthyroidism. In addition, TRAb remains persistently high in about 30% of patients with successful RAI outcome. Although neonatal hyperthyroidism was not developed in our population, the results of our study maybe taken into consideration in physicians who are to plan RAI for female patients with childbearing age.