Abstract
To evaluate the clinical and pathogenetic roles of TSH receptor antibodies in autoimmune thyroid diseases, TBII were measured by TSH-radioreceptor assay methods in 352 patients with Graves' disease, 108 patients with other thyroid diseases and 69 normal persons. The normal range of TBII activity was less than 15%. The frequencies of detectable TBII in 169 patients with untreated Graves' disease, 31 patients with hyperthyroidism under treatment and 70 patients with euthyrodism under treatment were 92.4%, 87.1% and 54.3% respectively. However 12 (21.8%) out of 55 patients who have been in remission more than one year after discontinuation of antithyroid drugs treatment had detectable TBII activities in their sera. In 196 patients with untreated Graves' disease, the frequency of TBII increased by increasing size of goiter and the frequency of proptosis was significantly high in patients whose TBII activities were more than 60%. TBII activities were roughly correlated with total $T_3,\;T_4$ and free $T_4$ index but low $\gamma^2$ value(less than 0.1). In 67 patients with Graves' disease who were positive TBII before antithyroid drugs treatment, TBII activities began to decrease from the third months and it was converted to negative in 35.8% of patients at 12 months after treatment. There were no significant differences of the declining and disappearing rates of TBII activities between high dose and conventional dose groups. TBII activities were significantly increased initially (2-4 months) and then began to decrease from 5-9 months after $^{131}I$ treatment. There were two groups, one whose TBII activities decreased gradually and the other did not change untill 12 months after subtotal thyroidectomy. Although preoperative clinical and laboratory findings of both groups were not different, TBII activities of non-decreasing group were significantly higher than those of decreasing group$(74.6{\pm}18.6%\;vs\;39.2{\pm}15.2%;\;P<0.01)$. Thirty three(55.9%) out of 59 patients with Graves' disease relapsed within 1 year after discontinuation of antithyroid drugs. The positive rate of TBII at the end of antithyroid drug treatment in relapse group(n=33) was significantly higher than those in remission group (n=26) (63.6% vs 23.1%; P < 0.05). The mean value of TBII activities at the end of antithyroid drug treatment in relapse group was significantly elevated $(29.7{\pm}21.4%\;vs\;14.7{\pm}11.1%,\;P<0.05)$. Positive predictive value of TBII for relapse was 77.8%, which was not different from those of TRH nonresponsiveness(78.6%). The frequencies of detectable TBII in 68 patients with Hashimoto's thyroiditis, 10 patients with painless thyroiditis and 5 patients subacute thyroiditis were 14.7%, 20% and 0%, respectively. However in 25 patients with primary nongoitrous myxedema, 11 patients(44%) showed TBII activities in their sera. 9 out of 11 patients who had TBII activities in their sera showed high TBII activities(more than 70% binding inhibition) and their IgG concentrations showing 50% binding inhibition of $^{125}I-bTSH$ to the TSH receptor were ranges of 0.1-2.6 mg/dl. One patient who had high titer of TBII in her serum delivered a hypothyroid baby due to transplacental transfer of maternal TBII. These findings suggested that 1) TSH receptor antibodies are closely related to a pathogenetic factor of Graves' hyperthyroidism and of some patients with primary non-goitrous myxedema, 2) measurement of TSH receptor antibodies is helpful in evaluating the clinical outcome of patients with Graves' disease during antithyroid drug treatment and in predicting the neonatal transient hypothyroidism of baby delivered from primary myxedema patients. 3) there are 2 or more different types of TSH receptor antibodies in autoimmune thyroid diseases including one which stimulates thyroid by binding to the TSH receptor and another which blocks adenylate cyclase stimulation by TSH.