Thyroxine, methimazole, and thyroid microsomal autoantibody titres in hypothyroid Hashimoto's thyroiditis.

Ten hypothyroid patients with Hashimoto's thyroiditis were treated with methimazole 30 mg in addition to thyroxine 0.15 mg daily. Another 10 hypothyroid patients with Hashimoto's thyroiditis were given thyroxine 0.15 mg alone. After 22 weeks of treatment significant decreases in thyroid microsomal autoantibody titres were observed in both groups (p less than 0.01). There was no difference in the mean change in titre between the two groups. When the patients treated with methimazole were subsequently given thyroxine 0.15 mg alone for a further 22 weeks no additional change in titre was observed. The data suggest that thyroxine, by normalising serum thyroid stimulating hormone concentrations, may reduce the autoantigenic properties of the thyrocytes with a subsequent decrease in autoantibody titres.