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


METHODS
Retrospective study.


METHODS
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).


METHODS
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 micrograms/day. Levothyroxine was discontinued in the 3 patients whose TSBAb activity disappeared. Two of them remained euthyroid, and 1 became hypothyroid.


CONCLUSIONS
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.
Yoshida
K
K
Department of Clinical and Laboratory Medicine, Tohoku University School of Medicine, Sendai, Japan.
Aizawa
Y
Y
Kaise
N
N
Fukazawa
H
H
Kiso
Y
Y
Sayama
N
N
Hori
H
H
Nakazato
N
N
Tani
J
J
Abe
K
K
D000704:Analysis of Variance; D001323:Autoantibodies / Q000097:blood*; D006111:Graves Disease / Q000532:radiotherapy*; D006801:Humans; D007037:Hypothyroidism / Q000276:immunology*; D018828:Immunoglobulins, Thyroid-Stimulating / Q000276:immunology*; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D008875:Middle Aged; D011989:Receptors, Thyrotropin / Q000097:blood; D012189:Retrospective Studies; D013972:Thyrotropin / Q000276:immunology*; D013997:Time Factors
D001323:Autoantibodies; D018828:Immunoglobulins, Thyroid-Stimulating; D007457:Iodine Radioisotopes; D011989:Receptors, Thyrotropin; C094372:thyrotropin-binding inhibitory immunoglobulin; D013972:Thyrotropin