Changes in the Properties of the Thyrotropin Receptor Antibody in Patients with Graves’ Disease after Radioiodine Treatment

We investigated the effect of a single dose of 131I upon thyrotropin receptor antibodies (TRAb) in 21 patients with Graves' disease. The thyrotropin receptor antibodies were assessed by parallel measurements of thyrotropin binding inhibitor immunoglobulin (TBII), thyroid stimulating antibody (TSAb), and thyroid stimulation blocking antibody (TSBAb) in serum by radioreceptor assay, stimulation of adenylate cyclase and inhibition of TSH-stimulated adenylate cyclase activation in FRTL-5 cells, respectively. Prior to radioiodine treatment TBII was detected in all 21 patients and TSAB in 19 patients. After radioiodine treatment TBII activities did not change during 12 months observation period, but in eight patients TSAb activities gradually decreased and were undetectable at the end of a 12 month observation period. Persistence of TSAb was not associated with clinical outcome. Eight patients developed hypothyroidism within 1 year after radioiodine treatment. Three of the hypothyroid patients developed TSBAb, and the appearance of TSBAb coincided with the development of hypothyroidism. These results suggest that TSBAb might develop after radioiodine treatment in a minority of patients with Graves' disease, and that the appearance of TSBAb, in addition to radiation induced thyroid destruction, might be involved in the development of hypothyroidism following radioiodine treatment.