Low prevalence of thyrotropin receptor antibody in primary hypothyroidism in Japan

The prevalence of TSH receptor antibody (TRAb), measured by RRA assay (TSH-binding inhibitor immunoglobulin, TBII) and biological stimulation-blocking assay (thyroid-stimulation blocking antibody, TSBAb), was examined in 134 consecutive patients with primary hypothyroidism due to autoimmune thyroiditis [83 patients with goitrous Hashimoto's disease (group A) and 51 with primary atrophic hypothyroidism (group B)]. In group A, TBII was detected in 6 patients (7%), TSBAb in 7 (8%), and both in 4 (5%). Similarly, in group B, TBII was detected in 7 patients (14%), TSBAb in 7 (14%), and both in 5 (10%). TBII with TSBAb activity was low or moderate in group A, but strongly positive in group B. No relationship was apparent in either group between TBII or TSBAb activity and any clinical or laboratory parameter examined. Moreover, no clinical or laboratory findings distinguished patients with TRAb from those without. The low prevalence of TRAb in primary hypothyroidism suggests that intrathyroidal cell-mediated destructive mechanisms may be more important in the pathogenesis of hypothyroidism in autoimmune thyroiditis.