A case of total thyroxine-binding globulin deficiency with Graves' disease: fluctuations of plasma triiodothyronine/thyroxine ratio.
A 37-year-old male with total thyroxine-binding globulin (TBG) deficiency associated with Graves' disease is described. Both TBG immunoreactivity and TBG capacity were not detectable in his serum. Serum concentrations of thyroxine-binding prealbumin and albumin were normal. He was initially hyperthyroid. During methimazole-treatment he was maintained in an euthyroid state except for two short hypothyroid periods. His plasma triiodothyronine/thyroxine (T3/T4) ratios during both the untreated hyperthyroid and the methimazole-induced hypothyroid states were higher than those during his methimazole-induced euthyroid state. These findings on changes in his T3/T4 ratio accompanying thyroidal dysfunction were qualitatively comparable with those in patients with Graves' disease with normal TBG levels: that both untreated hyperthyroid and methimazole-induced hypothyroid patients showed higher T3/T4 ratios than methimazole-induced euthyroid patients. These results may provide indirect evidence that changes in hormonal secretion and conversion that raise T3/T4 ratio can occur in thyroidal dysfunctions even in the complete absence of TBG.
D000328:Adult; D006111:Graves Disease / Q000097:blood*; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood; D007037:Hypothyroidism / Q000097:blood; D008297:Male; D008713:Methimazole / Q000494:pharmacology; D013963:Thyroid Hormones / Q000378:metabolism; D013974:Thyroxine / Q000097:blood*; D013975:Thyroxine-Binding Proteins / Q000172:deficiency*; D014284:Triiodothyronine / Q000097:blood*
D013963:Thyroid Hormones; D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine; D008713:Methimazole; D013974:Thyroxine