Thyroid histology of hyperthyroid Graves' disease with undetectable thyrotropin receptor antibodies

To determine the histological characteristics of hyperthyroid Graves' disease with undetectable TSH receptor antibodies (TRAb), we examined the thyroid histological findings of patients with hyperthyroidism who were referred for subtotal thyroidectomy and who lacked circulatory TRAb. Four patients had undetectable TRAb (6.4 +/- 4.2%) before treatment (group A). Their pathological and clinical findings were compared with those of four patients who had hyperthyroid Graves' disease with detectable TRAb (83.8 +/- 8.3%) before treatment (group B). The groups were matched for sex, age, duration of antithyroidal drug therapy, anti-Tg antibody, and antimicrosomal antibody levels. All patients were in a euthyroid state just before operation. Papillate hyperplastic epithelia in group A were significantly less severe than in group B. Enlarged colloids were not observed in two of the four patients in group A but were observed in all four patients in group B. Moderate or marked lymphocytic infiltrations were observed in all patients in group A but were virtually absent in group B. Based on these results, it is probable that hyperthyroid Graves' disease with undetectable TRAb titers represents an early stage or subtype of usual hyperthyroid Graves' disease in which there is marked or moderate lymphocytic infiltration.