ANTITHYROID HORMONE ANTIBODIES INDUCED BY INTERFERON-ALPHA

A 40-yr-old woman known for a multinodular goiter had hyperthyroidism. Treatment with antithyroid drugs and iodine therapy was effective. One year later, she received interferon-alpha for treatment of essential cryoglobulinemia. At that time, the patient was euthyroid. Testing for antithyroglobulin, antimicrosome, anti-TSH receptor, and antithyroid hormone antibodies was negative. After a 1-yr course of interferon-alpha, goiter enlargement was noticed. Apparently elevated free T3 and T4 serum values were measured by RIA, contrasting with clinical euthyroidism and normal TSH values. High serum levels of antithyroid hormone antibodies were found in the patient's serum, using a radio-labeled hormone immunoprecipitation assay. Antithyroglobulin and antimicrosome antibodies titers were also elevated and paralleled antithyroid hormone antibodies. After cessation of interferon-alpha therapy, clinical status and TSH levels remained normal, while thyroid hormone values and antithyroid hormone antibody levels progressively normalized. To our knowledge, this is the first report of antithyroid hormone antibodies induced by interferon-alpha. Since thyroid dysfunction is described in 10-15% of treated patients, the fact that interferon-alpha can induce antithyroid hormone antibodies has important implications: 1) the prevalence or intensity of thyroid dysfunction could be overestimated; and 2) artifactually elevated free T3 and T4 serum values could lead to inappropriate therapy of thyroid disease or cessation of interferon treatment.