Paired determination of thyroid-stimulating and TSH-binding inhibitory activities in patients with Graves' disease during antithyroid drug treatment.

Sequential changes in thyroid-stimulating antibodies (TSAb) and TSH-binding inhibitor immunoglobulins (TBII) during antithyroid drug treatment were studied in 17 patients with Graves' disease. Before treatment, TSAb and TBII were detected in 17 (100%) and 13 (76.5%) patients, respectively, with a significant correlation between the two activities (r = 0.600, n = 17, P less than 0.02). In 9 patients who became euthyroid as early as after 1-4 months of treatment, the TSAb and TBII activities both gradually decreased, and there was a good correlation between the changes of these activities during treatment. Among the 7 patients in whom small changes in TSAb and TBII activities were observed, 4 showed poor control of the thyrotoxicosis during the whole observation period (7 months-2 years). One patient who showed a marked dissociation between the changes in TSAb and TBII activities developed hypothyroidism, when his TBII became remarkably high. These potent TBII inhibited cAMP production induced by bTSH. These findings indicate that 1) changes in TSAb and TBII activities reflect the clinical course of hyperthyroidism in most patients with Graves' disease, and 2) development of a blocking-type of TBII may induce hypothyroidism in some patients after the treatment.