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

Summary

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: ΔT₃ (peak T₃ minus basal T₃), % increase in T₃ (peak over basal), and the ratio of T₃ to ΔTSH. 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.

Key words

Thyroid - TRH - Graves' disease