Thyroid dysfunction induced by interferon therapy for the treatment of hepatitis type C. A report of 4 cases.

We describe 4 patients with onset or aggravation of thyroid dysfunction induced by interferon (IFN) treatment of hepatitis type C. All 4 patients were females; 2 had hyperthyroidism and 2 had hypothyroidism during or after IFN therapy. The onset or aggravation of thyroid dysfunction occurred during administration of IFN in 1 patient and 4 weeks after the end of IFN therapy in the remaining 3 patients. The 2 patients who demonstrated hyperthyroidism were euthyroid and negative for thyroid autoantibodies before receiving IFN therapy. The remaining 2 patients who demonstrated hypothyroidism were positive for thyroid autoantibodies before IFN therapy. One of these patients had a slight decrease in thyroid function before IFN therapy. Anti-thyroid stimulating hormone (TSH) receptor antibodies became positive in all 4 patients. Since there may have been a causal relationship between IFN therapy and the onset or aggravation of thyroid dysfunction, IFN therapy should be administered with caution.