Exacerbation of thyroid autoimmunity by interferon alpha treatment in patients with chronic viral hepatitis: our studies and review of the literature.

In the present studies, the long term effects of IFN alpha on thyroid function and thyroid autoantibodies were evaluated in 42 patients with chronic viral hepatitis type C treated with IFN alpha for at least 4 months. Before IFN treatment, 41 patients tested were all euthyroid. Five (12%) out of 24 patients tested had positive tests for thyroid autoantibodies. MCHA/TPOAb was detected in all 5 and TGHA/TGAb in 3 out of these 5 patients. Six to 10 x 10(6) units (U) of recombinant or natural IFN alpha were given intramuscularly daily for the first 2 to 4 weeks, followed by 3 to 10 x 10(6) U thrice weekly for the subsequent 14 to 22 weeks. Thyroid dysfunction and/or rises in titers of thyroid autoantibodies were observed in 6 patients during IFN alpha treatment; clinically overt thyroid dysfunctions, destructive thyroiditis and thyrotoxicosis of unidentified etiology, developed in 2 patients 4 to 5 months after start of IFN treatment, subclinical hypothyroidism with a slight increase in serum TSH concentrations but no serum thyroid hormone alternations was observed in 2 patients, and increases in titers of thyroid autoantibodies without thyroid dysfunction were found in 2 patients. Thus, IFN alpha exacerbated thyroid autoimmunity exclusively in all patients with positive tests for thyroid autoantibodies prior to treatment, but did not induce thyroid autoimmunity in thyroid autoantibody-negative patients. These data suggest that the prolonged IFN alpha therapy can lead to exacerbation of thyroid autoimmunity in susceptible (thyroid autoantibody-positive) patients.