Susceptibility to thyroid disorders in hepatitis C.

BACKGROUND & AIMS: Autoimmune thyroid disorders (AITDs) are reported, especially during interferon treatment, in chronic HCV infection, in which non-organ-specific autoantibodies (NOSAs) are common. We wondered whether seropositivity for NOSA is associated with susceptibility to AITDs. METHODS: We evaluated thyroid function and antithyroglobulin and antithyroperoxidase antibodies in 348 Italian patients with chronic hepatitis C (34% NOSA-positive), 196 patients (33% NOSA-positive) of whom received interferon treatment. RESULTS: At baseline, thyroid disorders were significantly more frequent in liver/kidney microsomal antibody type 1 (LKM1)-positive patients (29% vs 9%, P < .005). Similarly, on interferon therapy de novo autoimmune thyroid markers and/or symptomatic thyroid disorders appeared more often in LKM1-positive patients (50% vs 3%, P < .0001). Both female sex and LKM1 positivity were predictors of AITD, but only the latter remained significant after logistic regression analysis. Cross-reactivity to all 7 linear epitopes encoding homologous amino acid sequences shared by the HCV polyprotein, CYP2D6 (the LKM1 autoantigen), and thyroperoxidase was detected in 86% LKM1-positive HCV patients with clinical thyroid disorders, but in none of the LKM1-positive or negative HCV patients without thyroid disease, and none of an HCV-negative control group comprising subjects with LKM1-positive autoimmune hepatitis or AITD without liver disease ( P < .0001). CONCLUSIONS: Patients receiving interferon therapy for hepatitis C seropositive for LKM1 are susceptible to develop AITDs, in association with treatment. Molecular mimicry and epitope spreading are potential pathogenic mechanisms.