Euthyroid Graves' disease showing no thyroid abnormalities except positive thyroid-stimulating antibody (TSAb): two case reports.

We report two cases of euthyroid Graves' disease in women who had ophthalmopathy without previous history of hyperthyroidism. Enlargement of extraocular muscles was observed by magnetic resonance imaging (MRI). The patients had no thyroid enlargement and their serum concentrations of free T4, free T3, and TSH were normal. The sera were negative for antithyroid microsomal and thyrogobulin antibodies, and anti-TSH receptor antibodies measured by radioreceptor assay. T3 suppression test results were normal. Only thyroid-stimulating antibody (TSAb) measured by sensitive bioassay was positive. These findings indicate that sensitive TSAb is the most useful laboratory test in the diagnosis of euthyroid Graves' disease.