Reduction of anti-thyroid hormone autoantibodies through plasma exchange and corticosteroid therapy

Anti-thyroid hormone autoantibodies are occasionally found in Hashimoto's disease. They can interfere with thyroid hormone assays. The authors report the case of a 35-year-old hypothyroid (TSH between 29 and 46 microIU/ml) female patient with Hashimoto's disease and surprisingly high free and total levels of plasma T4 and T3 assayed with different solid phase radio-immunologic kits. Two immunoenzymologic assay kits gave a T4 level close to the one expected. The presence of circulating anti-T4, T3 and reverse T3 autoantibodies was demonstrated by precipitating the corresponding tracers with the patient's serum in the presence of polyethylene glycol without heterologous antibodies. The replacement treatment of 150 micrograms l-thyroxine allowed normalization of TSH at 3.4 microIU/ml, but the patient remained tired and anxious, with headaches and tachycardia. After discontinuing treatment for one month a series of four plasma exchanges was carried out in six days. After the first exchange the binding percentages were already much lower and went even lower after the other exchanges. After the fourth one, the free T4 and T3 levels were closer to the expected levels:7.3 pmol/l (N:10-30 pmol/l) and 4.3 pmol/l (N:3-9 pmol/l). Treatment by prednisone made it possible to maintain the percentages of binding to the three tracers for two weeks at the levels reached after the fourth plasma exchange. Two months after discontinuing corticosteroid treatment they returned to the initial levels and were again interfering with the free T4 and T3 assays. This finding suggests that usefulness of the thyroid hormone immuno-enzymologic assay, which apparently is not affected by the anti-thyroid hormone autoantibody interference.(ABSTRACT TRUNCATED AT 250 WORDS)