Medical therapy of Graves' disease: effect on remission rates of methimazole alone and in combination with triiodothyronine

In a prospective. randomized study of 135 newly diagnosed patients with hyp erthyroidism due to Graves' disease we compared the effect on remission rat es of additional triiodothyronine (T3) with conventional antithyroid drug t herapy. To this end 114 patients were followed for at least 12 months (15.7 +/- 4.9, mean +/- S.D.) after the discontinuation of any therapy. After re turn of thyroid function to normal (8.5 +/- 7.4 weeks, mean +/- S.D.) patie nts were maintained on antithyroid medication for 9.0 +/- 2.5 months, They were then randomly assigned to one of three groups: group 1 (n = 44) stoppe d methimazole, groups 2 (n = 39) and 3 (n = 31) continued with exogenous T3 (not exceeding 75 mu g/day in any patient) for a further 6 months either w ith (group 2) or without (group 3) a fixed dose of 10 mg methimazole daily. The T3 dose was kept variable to keep TSH suppressed (< 0.1 mU/l), which c ould be achieved in 82% of patients on 100% of their monthly visits. No ser ious side-effect requiring the discontinuation of the study occurred in any patient. Total T3, TSH-receptor antibodies and some previously suggested p otential predictors of relapse including thyroid size by ultrasound, 24h ur inary iodine excretion, history of cigarette smoking and ophthalmopathy wer e determined at the outset of the study and subsequently every 6 months (an d total T3 every 4 weeks). No significant difference (P > 0.05, Chi square) was seen in relapse of hyp erthyroidism after a mean follow-up of 16 months (range: 12-31 months; grou ps 1: 52%, 2: 44% and 3: 42%) in an area of low-to-moderate iodine intake p revalence of 24 h urinary iodine excretion < 100 mu g/24 h: 17 and 25% at t wo different measurements respectively). Concomitantly, no predictor of rec urrence of disease could be identified, irrespective of treatment modality.