1990 Volume 37 Issue 6 Pages 769-775
The present study was undertaken to evaluate whether the normalization of the serum TSH level in a supersensitive assay during the initial treatment with antithyroid drugs (ATD) is a useful indicator for the reduction of the initial dose of ATD in 50 patients with hyperthyroidism due to Graves' disease.
The initial dose of ATD was continued until the achievement of the euthyroid state, and was then reduced either before the serum TSH level was in the normal range in 9 of 29 patients treated with methimazole (MMI)(group MMI-1) and 8 of 21 treated with propylthiouracil (PTU)(PTU-1), or after the serum TSH level was in/above the normal range in 20 of 29 treated with MMI (MMI-2) and 13 of 21 treated with PTU (PTU-2). Although there were no significant differences in age, sex, thyroid function, prevalence of autoantibodies, goiter size, duration of the disease or the initial and modified doses of ATD, the mean durations of the administration of the initial dose of ATD in MMI-2 and PTU-2 were significantly longer than those in MMI-1 and PTU-1, respectively. As a result, 4 (44%) in group MMI-1, 20 (100%) in MMI-2, 2 (25%) in PTU-1 and 7 (54%) in PTU-2 developed low free T4 levels, and 1 (11%) in MMI-1, 15 (75%) in MMI-2 and 3 (23%) in PTU-2 developed low free T3 levels. Serum TSH levels increased over the normal range in 3 (33%) in MMI-1, 18 (90%) in MMI-2 and 5 (39%) in PTU-2.
The incidences of low free thyroid hormone levels and TSH increase in MMI-2 were significantly higher than those in all the other groups, and the incidence of TSH increase in PTU-2 was significantly higher than that in PTU-l. The mean values for peak TSH in patients whose serum TSH increased to over the normal range were 43.7μU/mL in MMI-1, 43.3 in MMI-2 and 18.2 in PTU-2.
These data demonstrate that the administration of the initial dose of ATD (particularly MMI) until the normalization of the serum TSH level causes a high incidence of the hypothyroid state.
