Hepatitis C viral infection and thyroid diseases.

Introduction. - The combination of hepatitis C virus (HCV) infection and th yroid diseases raises several issues that are the prevalence of thyroid aut oimmunity in patients with chronic hepatitis C, the prevalence of HCV infec tion in patients with autoimmune thyroid diseases, and the effect of interf eron alpha treatment on thyroid function in chronic HCV hepatitis. Current knowledge and key points. - The prevalence of anti-antibodies range s from 4.6 to 15% in HCV infection, which is considered as significant by v arious authors. Results have to be interpreted according to the following: the type of auto-antibodies detected, the age, sex, ethnic origin of the po pulation studied, and characteristics of the control population. Recent dat a are suggestive of a high prevalence of anti-thyroid auto-antibodies in fe males with HCV infection. An increased prevalence of HCV infection in patie nts with Hashimoto's thyroiditis is not confirmed. During treatment of chro nic hepatitis C. interferon alpha induces thyroid dysfunctions (3 to 15% of the cases) with various clinical presentations. Hypothyroidism is more com mon (two out of three cases) than hyperthyroidism (one out of three cases). Hyperthyroidism followed by hypothyroidism has also been described. Clinic al symptoms vary, ranging from subclinical to severe manifestations. Thyroi d dysfunction may be delayed after discontinuation of the interferon treatm ent. Hypothyroidism is easily cured by L-thyroxine replacement therapy when necessary, and regression may be observed following discontinuation of int erferon treatment. Each case of hyperthyroidism has to be precisely evaluat ed. Development of anti-thyroid antibodies or an increase in anti-thyroid a ntibodies titers is often observed during interferon alpha treatment, thus suggesting the existence of immunological mechanism at the origin of thyroi d dysfunction. Futhermore, interferon would directy act on iodine. Future prospects and projects. - Clinical studies are still necessary to be tter clarify the links between HCV infection and thyroid autoimmunity and t o determine risk factors for the development of thyroid dysfunction during interferon alpha therapy. The effects of HCV and interferon alpha on thyroi d autoimmunity and function have to be investigated in basic research. (C) 1999 Elsevier, Paris.