Graves’ disease and Hashimoto’s thyroiditis: effects of high doses of antithyroid drugs on thyroid autoantibody levels

Abstract

We studied the effects of high doses of methimazole (MMI) or propylthiouracil (PTU) on thyroid-stimulating antibody (TSAb), antithyroid microsomal (MCHA) and antithyroglobulin (TGHA) levels in Graves’ disease and Hashimoto’s thyroiditis. Thirty Graves’ hyperthyroid patients were treated for 14 ± 8 months (mean ± SD) with MMI, 60–80 mg daily or PTU, 900–1200 mg daily plus T3, 50–75 μg daily. Fifteen Hashimoto’s thyroiditis patients (4 of whom hypothyroid) received 100–200 μg of T4 daily for 4–8 weeks prior to MMI, 60–90 mg daily or PTU, 900 mg daily for 12–16 weeks. In Graves’ disease a decrease (p < 0.001) in TSAb activity (20/25 patients) was observed: before therapy, 0.424 ± 0.506 pmoles/mg wet wt and at the end of treatment, 0.189 ± 0.23 pmoles/mg wet wt. The MCHA titers also fell (18/26 patients) from 1:10,403 ±20,197 to 1:3,476 ± 5,252 (p < 0.01) and was associated with a decrease in free T4 values (1.23 ± 0.69 vs. 0.51 ± 0.36 ng/di; p<0.01). A fall of MCHA titers in T4-treated Hashimoto’s thyroiditis patients (1:10,416 ± 25,576) was found when compared with the value before T4 (1:25,920 ± 39,973; p < 0.001). However, the titers of MCHA (1:13,280 ± 25,992) did not change on MMI or PTU plus T4 treatment. The TGHA titers fell in a single patient. No alterations were observed in serum immunoglobulins. Serum concentrations of the complement factor C’3 remained higher (p < 0.01) than normal values in both Graves’ disease and Hashimoto’s thyroiditis. In conclusion, our data suggest that MMI and PTU have no influence on the immune system as a whole and the thyroid antibodies fall is due to a reduced thyroid antigen availability to the immune system and secondarily depends on the euthyroid status rather than on the antithyroid drug effect by itself.