Vasculitis improving with interferon therapy. Extrahepatic manifestations of hepatitis C virus (HCV) infection include cryoglobulinemia, membranous glomerulonephritis, porphyria cutanea tarda, and polyarteritis nodosa. Reduction in immune complex formation has been associated with improvement in symptoms. This patient illustrates the improvement of cryoglobulinemia with interferon therapy for HCV. The patient's vasculitis core improved as HCV-RNA levels decreased. After interferon was stopped, there was recurrence of HCV-RNA along with a worsening of the patient’s vasculitis score. Anti-HCV—antibodies to HCV. (Adapted from Misiani et al. [61].