Effect of interferon-beta on thyroid function in patients of chronic hepatitis C without preexisting autoimmune thyroid disease

The effect of interferon-beta (IFN-beta) on thyroid function was studied in patients with chronic hepatitis who had no preexisting thyroid disease. Eleven patients (9 males and 2 females) aged 20 to 65 years, with a mean age of 47.7 +/- 13.5 years, were treated with 6 million units of IFN-beta intravenously every day for 8 weeks. During IFN-beta administration (4th to 8th week of treatment), both serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations decreased significantly (P<0.0005 and P<0.05, respectively): FT4, 1.37 +/- 0.17 to 1.09 +/- 0.12 ng/dl, and FT3, 3.71 +/- 0.45 to 3.28 +/- 0.34 pg/ml. On the other hand, serum TSH increased significantly from a baseline of 1.70 +/- 0.82 to 3.34 +/- 1.98 mu U/ml during IFN-beta administration (P<0.005). Four to eight weeks after cessation of treatment, the mean serum FT4 concentration was similar to that during IFN-beta administration (1.04 +/- 0.14 ng/dl), but mean serum FT3 and TSH concentrations returned to pre-treatment levels (FT3, 3.57 +/- 0.42 pg/ml and TSH, 1.60 +/- 0.84 mu U/ml). Both reverse T-3 and thyroglobulin were essentially unchanged. Tests for anti-thyroglobulin and anti-microsomal antibodies were negative in all the patients. These results indicate that IFN-beta may inhibit thyroid function in patients without preexisting thyroid disease irrespective of humoral immune responses.