Lung disease and hepatitis C virus infection

Idiopathicpulmonary fibrosis (IPF) is a relatively uncommon disease with a generally poor prognosis. Fifty per cent of patients diagnosed as having IPF may be expected to die within 4 years of the diagnosis. Although the etiology of IPF is unknown, it has been suggested that viral agents, among which hepatitis C virus (HCV), may be involved in pathogenesis of the disease. Several investigators have suggested that HCV infection is associated with various clinical conditions. These include mixed cryoglobulinemia (MC), autoimmune thyroiditis, porphyria cutanea tarda, membranoproliferative glomerulonephritis, sicca syndrome, non-Hodgkin's lymphoma, and IPF. According to the available data, HCV infection appears to be main triggering factor of MC, which in rare cases may be complicated by clinically overt lung fibrosis, while the data for the association between HCV infection and IPF remain still weak. However, a number of anecdotal observations together with the example of lung fibrosis in the setting of MC are quite intriguing. Further studies including different HCV-positive patients' subsets are necessary to ascertain the exact role of this virus in both secondary and idiopathic lung fibrosis. Here, the literature on the possible association between HCV and various immuno-mediated extrahepatic disorders, with particular attention to lung fibrosis, has been widely reviewed.