The Prognosis of Graves' Disease After Antithyroid Drug Treatment

Clinical Significance of the T₃ Suppression Test and Abnormal Thyroid Stimulators

Abstract

The prognostic significance of both the triiodothyronine (T₃) suppression test and the detectability of thyroid stimulating immunoglobulins in patients with Graves' disease who had been treated with antithyroid drugs was evaluated.
Eighty-three patients underwent a T₃ suppression test after having been euthyroid for at least 6 months. In 33 patients, the human thyroid stimulator (HTS) was assayed by measuring cyclic AMP increase in cultured thyroid adenoma cells, and TSH-binding inhibitor immunoglobulins (TBII) were measured by using the radioreceptor assay of TSH. Among 43 patients who had discontinued the drug treatment, 37 patients were under observation for 6-42 months.
When a fall in 30-minute thyroid ^99m TcO₄^-uptake of 50% or more after T₃ administration was defined as positive suppression, the relapse rate was 30% in non-suppressive cases and 26% in suppressive cases. The relapse rate was lower in cases whose pre-suppression uptake was less than 3.0% (3 out of 17 patients) or in cases whose uptake after T₃ administration was less than 0.8% (1 out of 9 patients).
Of 15 patients with negative suppression, 5 (33.3%) were positive in HTS and 4 (26.7%) were positive in TBII. On the other hand, two (11.1%) each of 18 patients with positive suppression were positive in HTS and TBII respectively. Neither HTS nor TBII had been detected at the cessation of therapy in any of the 12 patients who remained euthyroid during the follow-up period. On the other hand, four (44.4%) out of 9 patients who relapsed had been positive in either HTS or TBII. Thus the Graves' disease specific immunoglobulins were found to be significantly associated with the relapse of the disease (p<0.05).
The above data indicates that regardless of the suppressibility of ^99mTcO₄^-uptake after T₃ administration, the rate of recurrence is high when the uptake after T₃ is more than 0.9% and/or when either HTS or TBII are positive.