Sensitivity of Thyroids to Endogenous Thyrotrophin in Patients with Graves' Disease

Abstract

T3 nonsuppressibility and TSH nonresponsiveness to TRH are characteristics of untreated hyperthyroid Graves' disease. Although the tests are commonly restored to normal during antithyroidal drug therapy, dissociation of TRH and T3 suppression tests have been observed in euthyroid Graves' disease and during drug therapy. Abnormalities of pituitary-thyroidal regulation and persistence of thyroid autoimmune disease have been found in Graves' patients following various modalities of therapy. The present study investigated in vivo sensitivity to endogenous TSH of thyroids in 144 Graves' disease patients following treatment with subtotal thyroidectomy, 131I, or antithyroidal drugs. After administration of TRH, thyroidal sensitivity to TSH was determined by the following: delta T3 (peak T3 minus basal T3), % increase in T3 (peak over basal), and the ratio of delta T3 to delta TSH. Significant differences in sensitivity to TSH in T3 nonsuppressible patients were found compared to suppressible patients regardless of their TSH responses to TRH or modality of therapy. These data suggest that measurements of serum T3 and TSH following TRH administration to determine in vivo thyroidal sensitivity may be substituted for the T3 suppression test as a confirmatory test for Graves' disease or as a prognosticator of relapse following therapy.