Two cases of Graves' disease with anti-thyroid hormone antibodies

Abstract

We have experienced 2 cases of Graves' disease associated with anti-thyroid hormone auto-antibodies. Case 1: a 24-year-old pregnant woman was found to have exacerbation of Graves' disease of which she had been diagnosed when she was 10 years old. She was treated with propylthiouracil (PTU, 450mg/day) since March 26, 1985 when intra-uterine fetal death was found. Since serum total T₃ (TT₃) levels had been high even long after abortion in the face of normalization of total T₄ (TT₄), free T₄, and thyrotropin (TSH), presence of anti-thyroid hormone antibodies was suspected. Addition of labelled thyroid hormone to her serum followed by precipitation of γ-globulin fraction with 12.5% of polyethylene glycol showed an increased binding of ¹²⁵I-T₃ or ¹²⁵I-T₄r being 19.3% or 11.0%, respectively, to her serum γ-globulin fraction. Scatchard plot of anti-T₃ antibodies in her serum was analyzed in two components; one with a higher affinity constant (5.4×10⁷ M^-1), and the other with a lower affinity constant (1.0×10⁶ M^-1). Case 2: a 16-year-old female had been diagnosed as Graves' disease when she was 15 years old and had been treated with MMI for a year. By the treatment, she became physically euthyroid, and serum total thyroid hormone (TT₃, TT₄) levels declined to the normal level. However, since free thyroid hormone (FT₃, FT₄) levels showed unusually high levels, presence of anti-thyroid hormone antibodies in her serum was suspected. Her serum γ-globulin bound 34.5% and 12.2%, respectively, of ¹²⁵1-T₃ and ¹²⁵I-T₄. Scatchard plot of anti-T₃ antibodies in her serum was analyzed into two components; one with a higher affinity constant (2.4×10¹⁰ M^-1), the other with a lower affinity constant (3.1×10⁹ M^-1). Although further characterization of anti-T₄ antibodies in both cases has not been done, from the binding data of ¹²⁵I-T₄ to both sera, in addition to anti-T₃ antibodies, both cases were considered to have anti-T₄ antibodies. Our present cases indicate that it is clinically important to bear the presence of anti-thyroid hormone antibodies in mind to account for the possible error in measuring T₃ or T₄ by RIA. In the case that RIA results give unexpectedly high or low T₃ and/or T₄ value, the presence of autoantibodies should be considered first and a test for them is recommended.