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.