Changes in Serum Autoantibodies to Thyroid Peroxidase During Antithyroid Drug Therapy for Graves' Disease.

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Abstract
Thyroid microsomal antigen is considered to be identical with thyroid peroxidase (TPO). Although there have been many reports concerning changes in microsomal autoantibody during the course of antithyroid drug therapy for Graves'' disease, little is known about this matter in relation to TPO autoantibody (TPOab). Therefore, in this paper, we studied serial changes in the latter autoantibody. Initial levels of serum TPOab (% immunoprecipitation) in 13 patients with hyperthyroid Graves'' disease ranged from -11.3% to +84.5% (mean.+-.SD, 38.9.+-.31.8%). Of three patients with persistently increased serum TPOab throughout drug therapy, all had recurrence of hyperthyroidism after the drug was discontinued. Of seven patients whose TPOab levels were initially high but subsequently decreased, four had remission of the disease after drug therapy. Inhibition by TPOab of the TPO activity was also demonstrated by both guaiacol and iodide assays, and changes in this inhibitory activity during therapy varied among individuals. This inhibition was not corelated with disease remission. The decrease in serum TPOab observed in some antithyroid drug-treated patients may reflect a decline in disease activity or may be a direct effect of the drug.