Hepatitis C-associated mixed cryoglobulinaemia: a crossroad between autoimmunity and lymphoproliferation.

Hepatitis C virus (HCV) infection is the second most cocmmon chronic viral infection in the world with a global prevalence of about 2%. Chronic HCV infection is commonly associated with a number of extrahepatic complications. Circulating mixed cryoglobulins (MCs) are detected in 40-60% of HCV-infected patients whereas overt cryoglobulinaemia vasculitis develops in only 5-10% of the cases. MC reflects the expansion of B cells producing a pathogenic IgM with rheumatoid factor (RF) activity. Because cryoglobulin-producing B cells in HCV are mostly monoclonal, HCV-associated MC can be viewed as a benign B cell lymphoproliferative condition. The disease expression of MC vasculitis is variable, ranging from mild clinical symptoms (purpura, arthralgia) to fulminant life-threatening complications (glomerulonephritis, widespread vasculitis). The overall risk of non-Hodgkin's lymphoma in patients with HCV-MC is estimated to be 35 times higher than that in the general population. This review will focus on recent advances in our understanding of the clinical course, complications, pathophysiology and treatment of those immune-mediated disorders.