Hepatitis C virus has several potential extrahepatic manifestations. Four are known to cause kidney disease: membranous glomerulonephritis, polyarteritis nodosa, MPGN and essential mixed cryoglobulinemia (type 2 cryoglobulinemia). The last condition is also associated with a skin exanthem (see image above) and a neuropathy. This purpuric rash is due to the deposition of of an antigen-antibody complex in the small-caliber vasculature.
Cryoglobulinemia is most effectively treated with interferon, or in other words, by treating the underlying HCV infection. The combination of Ribavirin is preferred, but remember that Ribavirin use is contraindicated when there is significant renal impairment. Severe, acute disease may even require plasmapheresis (sometimes with the addition of glucocorticoids and cyclophosphamide to prevent new antibody formation).