Hepatitis C viral infection and thyroid diseases.

Introduction. - The combination of hepatitis C virus (HCV) infection and thyroid diseases raises several issues that are the prevalence of thyroid autoimmunity in patients with chronic hepatitis C, the prevalence of HCV infection in patients with autoimmune thyroid diseases, and the effect of interferon alpha treatment on thyroid function in chronic HCV hepatitis. Current knowledge and key points. - The prevalence of anti-antibodies ranges from 4.6 to 15% in HCV infection, which is considered as significant by various authors. Results have to be interpreted according to the following: the type of auto-antibodies detected, the age, sex, ethnic origin of the population studied, and characteristics of the control population. Recent data are suggestive of a high prevalence of anti-thyroid auto-antibodies in females with HCV infection. An increased prevalence of HCV infection in patients with Hashimoto's thyroiditis is not confirmed. During treatment of chronic hepatitis C. interferon alpha induces thyroid dysfunctions (3 to 15% of the cases) with various clinical presentations. Hypothyroidism is more common (two out of three cases) than hyperthyroidism (one out of three cases). Hyperthyroidism followed by hypothyroidism has also been described. Clinical symptoms vary, ranging from subclinical to severe manifestations. Thyroid dysfunction may be delayed after discontinuation of the interferon treatment. Hypothyroidism is easily cured by L-thyroxine replacement therapy when necessary, and regression may be observed following discontinuation of interferon treatment. Each case of hyperthyroidism has to be precisely evaluated. Development of anti-thyroid antibodies or an increase in anti-thyroid antibodies titers is often observed during interferon alpha treatment, thus suggesting the existence of immunological mechanism at the origin of thyroid dysfunction. Futhermore, interferon would directy act on iodine. Future prospects and projects. - Clinical studies are still necessary to better clarify the links between HCV infection and thyroid autoimmunity and to determine risk factors for the development of thyroid dysfunction during interferon alpha therapy. The effects of HCV and interferon alpha on thyroid autoimmunity and function have to be investigated in basic research. (C) 1999 Elsevier, Paris.