Long-Term Antithyroid Drug Treatment: Trends in Serum TSH and TSH Receptor Antibody Changes in Patients with Graves’ Disease

Objectives: trends in serum thyroid-stimulating hormone (tsh) and tsh receptor antibody (trab) changes during antithyroid drug treatment, and long-term prognosis were evaluated in graves’ hyperthyroidism (gd). methods: in 609gdpatients initially treated with 15mgof methyl-mercapto imidazole (mmi), the changes in serum trab and longterm prognosis were compared in the tsh-normalized group (a) and the tsh-suppressed group (b and c) during the initial 180 days of treatment. results: early responses to mmi during 180 days of treatment were as follows: 48 cases (7.9%) became hypothyroid with elevated tsh (a1), and 188 cases (30.9%) became euthyroid with normal tsh (a2). among patients with continuously suppressed tsh, the free t4 (ft4) level was low in 31 cases (5.1%) (b1-inappropriately suppressed tsh), ft4 and ft3 were normal in 185 cases (30.4%) (b2), ft4 was normal, but ft3 remained high in 84 cases (13.8%) (b3), and ft4 remained high in 73 cases (12.0%) (c-refractory). serum trab became negative after < 5 years then remained negative in 25% - 51% of the cases (smooth type), became negative after < 5 years then became positive again in 30% - 43% of the cases (fluctuating type), and remained positive after > 5 years in 10% - 42% of the cases (smoldering type). in total, remission occurred after 6.2 (3.0 - 10.4) years of treatment in 42%, possible remission on a small maintenance dosage of antithyroid drug occurred in 13%, and spontaneous hypothyroidism occurred in 4.4% of the cases. the smoldering type was more frequent in the b1 and c groups than in others, and remission was less frequent. the difference in the long-term prognosis depending on the early response to mmi disappeared after excluding the ablated patients. without ablation, remission or spontaneous hypothyroidism could be expected in 60% - 75% of patients after tenacious treatment for > 10 years. conclusions: prolonged suppression of serum tsh may suggest active trab activity during treatment, and continuous trab positivity for more than 5 years suggests persistent gd activity.