Role of thyroid-stimulating blocking antibody in patients who developed hypothyroidism within one year after 131I treatment for Graves' disease

ABSTRACT

 

OBJECTIVE

We recently reported that thyroid-stimulating blocking antibody (TSBAb) may not contribute to the development of hypothyroidism more than six years after ¹³¹I treatment. In the present study, we attempted to determine whether hypothyroidism that develops within a shorter period of time following ¹³¹I therapy is associated with TSBAb.

 

DESIGN

Retrospective study.

 

PATIENTS

Sera were obtained from 8 patients who developed hypothyroidism within 6 months after ¹³¹I therapy (Group 1), 8 patients who became euthyroid one year after ¹³¹I therapy (Group 2), and 7 patients who developed transient hypothyroidism (Group 3).

 

MEASUREMENTS

Thyroid stimulating antibody (TSAb) activity was measured as the amount of cyclic adenosine monophosphate (cAMP) produced by cultured FRTL-5 cells, and TSBAb activity as the inhibition of cAMP produced in response to 100 mU/l bovine TSH.

 

RESULTS

At about 3 months after ¹³¹I treatment, TSAb activity increased significantly in Groups 2 and 3, but did not change in Group 1. In contrast, TSBAb activity in Group 1 increased significantly and was positive in 6 patients at that time. At 12–18 months after ¹³¹I treatment, TSBAb activity tended to decrease and remained positive in 3 patients but became negative in 3 patients. It did not change in the patients in Groups 2 and 3. The patients in Group 1 were treated with levothyroxine, 75–125 μg/day. Levothyroxine was discontinued in the 3 patients whose TSBAb activity disappeared. Two of them remained euthyroid, and 1 became hypothyroid.

 

CONCLUSION

Results indicate that the hypothyroidism that develops within a short time after ¹³¹I treatment may be caused by TSBAb activity. Thyroid function may be recovered when TSBAb activity disappears.