Changes in thyroid-stimulating antibody activity in Graves' disease treated with antithyroid drug and its relationship to relapse: a prospective study.

Thyroid-stimulating antibodies (TSAb) were found in 51 patients (83.6%) with untreated Graves' disease. The mean TSAb index reached the normal level after 6 months of antithyroid drug therapy. In 9 patients (14.8%), TSAb remained persistently positive during and after antithyroid drug therapy, and relapse occurred in all. In 42 patients (68.8%), TSAb indices gradually returned to the normal range after drug treatment was started; in 38% of these, remission was maintained after treatment was stopped, in another 40.5%, relapse occurred when they were TSAb-positive, and the remaining 21.5% relapsed despite return of TSAb indices to the normal range. A positive TSAb index at the end of drug treatment was a useful indicator in predicting subsequent relapse because, with 1 exception, all patients who were still TSAb positive at drug withdrawal relapsed subsequently.