Thyroid-stimulating immunoglobulins in mixed (type II) cryoglobulinemia associated with thyrotoxicosis

The role of human parvovirus B19 and hepatitis C virus in the development of thyroid disorders

The presence of viruses in the thyroid has been shown, but whether they are implicated in thyroid diseases or are only spectators is under investigation. The most important candidate viruses for autoimmune thyroid disorders (AITD) are hepatitis C virus (HCV) and human parvovirus B19 (or Erythrovirus B19 or EVB19). Retrospective and prospective case-control studies conducted on pathology slides showed (by PCR, in situ hybridization or immunohistochemistry) EVB19 was present in thyroid tissues of patients with autoimmune thyroiditis (AT), Graves' disease and thyroid cancer. Though AITD can be associated with acute EVB19 infection, it is not clear whether EVB19 could have a pathogenetic role in autoimmune thyroid diseases pathophysiology. Many studies have shown that frequently, patients with HCV chronic infection (CHC) show elevated serum anti-thyroperoxidase (TPOAb) and/or anti-thyroglobulin autoantibodies levels, ultrasonographic signs of chronic AT, and subclinical hypothyroidism. In patients with HCV-associated mixed cryoglobulinemia (MC + HCV), AITD were more prevalent with respect to controls, and also vs HCV patients without cryoglobulinemia. Papillary thyroid cancer was more prevalent in MC + HCV or CHC patients than in controls, especially in patients with AT. Recently it has been shown an elevated incidence of new cases of AT and thyroid dysfunction in MC patients. These results suggest an attentive monitoring of thyroid function and nodules in HCV patients with risk factors (female gender, a borderline high initial thyrotropin, TPOAb positivity, a hypoechoic and small thyroid) for the development of thyroid disorders.

Autoimmune and neoplastic thyroid diseases associated with hepatitis C chronic infection

Frequently, patients with hepatitis C virus (HCV) chronic infection have high levels of serum anti-thyroperoxidase and/or anti-thyroglobulin autoantibodies, ultrasonographic signs of chronic autoimmune thyroiditis, and subclinical hypothyroidism, in female gender versus healthy controls, or hepatitis B virus infected patients. In patients with "HCV-associated mixed cryoglobulinemia" (MC + HCV), a higher prevalence of thyroid autoimmune disorders was shown not only compared to controls, but also versus HCV patients without cryoglobulinemia. Patients with MC + HCV or HCV chronic infection show a higher prevalence of papillary thyroid cancer than controls, in particular in patients with autoimmune thyroiditis. Patients with HCV chronic infection, or with MC + HCV, in presence of autoimmune thyroiditis, show higher serum levels of T-helper (Th)1 (C-X-C motif) ligand 10 (CXCL10) chemokine, but normal levels of Th2 (C-C motif) ligand 2 chemokine, than patients without thyroiditis. HCV thyroid infection could act by upregulating CXCL10 gene expression and secretion in thyrocytes recruiting Th1 lymphocytes that secrete interferon-γ and tumor necrosis factor-α. These cytokines might induce a further CXCL10 secretion by thyrocytes, thus perpetuating the immune cascade, which may lead to the appearance of autoimmune thyroid disorders in genetically predisposed subjects. A careful monitoring of thyroid function, particularly where nodules occur, is recommended in HCV patients.

Thyroid involvement in hepatitis C - associated mixed cryoglobulinemia

OBJECTIVE

The prevalence and clinical features of thyroid involvement in patients with hepatitis C virus-associated mixed cryoglobulinemia (MC+HCV) have been reviewed.

DESIGN

A PubMed Medline search was conducted through December 2011 to identify all studies that reported thyroid involvement in MC+HCV patients. Reference lists of the papers initially detected were manually searched to identify additional relevant reports. Studies had to contain sufficient and clear information to be included.

RESULTS

In MC+HCV patients, the following thyroid autoimmune abnormalities were significantly more frequent than in controls: high levels of serum anti-thyroperoxidase autoantibody (AbTPO); high levels of serum AbTPO and/or anti-thyroglobulin autoantibody; humoral and ultrasonographical signs of thyroid autoimmunity (35% vs 16%); prevalence of subclinical hypothyroidism (11% vs 2%). Also, the prevalence of papillary thyroid cancer has been found higher in MC+HCV patients than in controls, in particular in patients with autoimmune thyroiditis. The involvement of T helper 1 immunity and chemokine (C-X-C motif) ligand 10 (CXCL10) may be the pathogenetic basis of the association between MC+HCV and thyroid autoimmunity.

CONCLUSION

These results show a high prevalence of thyroid disorders in patients with MC+HCV and point to the need for careful monitoring of thyroid function in these patients.