Six of 50 (12%) patients with chronic hepatitis C who were treated with interferon developed thyroid disease or an autoimmune thyroid reaction while undergoing treatment. One patient developed silent thyroiditis, with an increase in serum tri-iodothyronine (T3), thyroxine (T4), free T3, free T4, and markedly suppressed thyroid-stimulating hormone (TSH) levels, accompanied by the appearance of both antithyroglobulin (TgAb) and antimicrosomal antibodies (McAb). One patient developed hypothyroidism in association with moderately elevated TSH levels and high titers of McAb. TSH, TgAb, and McAb levels returned to the initial values at least 4 months after the end of interferon treatment (9 months of follow up). Four patients whose TgAb and/or McAb levels were elevated during treatment with interferon had been diagnosed as having subclinical autoimmune thyroiditis; however, their thyroid function remained in the normal range. These results suggested that treatment with interferon can cause a transient autoimmune thyroid reaction and disease as a side effect.
