Serum thyrotropin-receptor autoantibodies levels after I therapy in Graves' patients: effect of pretreatment with methimazole evaluated by a prospective, randomized study.
OBJECTIVE
Radioiodine therapy (131I) in hyperthyroid Graves' disease is generally followed by a transitory increase in levels of thyrotropin receptors antibodies (TRAb). Immunosuppressive effects of antithyroid drugs are still a matter of debate. In this study we evaluated the effect of methimazole pretreatment on the TRAb boost induced by 131I.


METHODS
A randomized, prospective clinical trial.


METHODS
61 patients were randomly assigned to receive 131I alone (32 patients) or 131I plus pretreatment with methimazole (30 mg/day; 29 patients). Serum TRAb levels were measured on the day of 131I dosing (D0), and at 1, 3, 6 and 12 months after 131I administration.


RESULTS
The mean serum TRAb levels decreased significantly from baseline to D0 in patients treated with methimazole (80.8 vs 48.8 U/l; P<0.05). After 131I treatment, TRAb levels increased at 3 months (48.8 to 60 U/l; 19%) and they were still elevated at 6 months compared with D0 values (99.9 U/l; 105%). Thereafter, TRAb levels decreased to baseline values (47.8 U/l) at 12 months. In hyperthyroid patients, TRAb levels increased significantly from D0 to 1 month (45.0 to 78 U/l; 73%) reaching their highest levels at 3 months (225 U/l; 400%). After this, we observed a progressive decrease to the baseline levels at 12 months (40.0 U/l). The course of TRAb levels after 131I treatment was significantly different between the two groups (P<0.05). Multiple regression analysis identified serum TRAb levels on D0 as independent predictors of TRAb increment after 131I therapy (r2=0.34; P=0.001). A higher increment in serum TRAb levels was associated with hypothyroidism after 1 year of follow-up.


CONCLUSIONS
Methimazole pretreatment attenuates the 131I-induced rise in serum TRAb levels. The effects of methimazole could be attributed to a direct immunomodulatory action or may be due to its effects on the control of hyperthyroidism, which is a known cause of immune dysregulation.
Endocrine Division, Hospital de Clinicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2350, 90035-003 Porto Alegre, RS, Brazil.
Vania A
VA
Andrade
Jorge L
JL
Gross
Ana Luiza
AL
Maia
D000328:Adult; D013956:Antithyroid Agents / Q000627:therapeutic use*; D001323:Autoantibodies / Q000097:blood; D003131:Combined Modality Therapy; D005260:Female; D005500:Follow-Up Studies; D006111:Graves Disease / Q000188:drug therapy* / Q000276:immunology / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008713:Methimazole / Q000627:therapeutic use*; D008875:Middle Aged; D011446:Prospective Studies; D011989:Receptors, Thyrotropin / Q000276:immunology*
D013956:Antithyroid Agents; D001323:Autoantibodies; D007457:Iodine Radioisotopes; D011989:Receptors, Thyrotropin; D008713:Methimazole