Background: Previous studies on membranoproliferative glomerulonephritis (MPGN) and cryoglobulinemic glomerulopathy (CG) were based upon case series that were performed before hepatitis C virus (HCV) infection was routinely investigated. Therefore, it remains unknown how far HCV contributes to MPGN or CG, and there have only been a few reports about HCV-negative idiopathic MPGN.
Patients and methods: Thirty-five patients with MPGN diagnosed by renal biopsy who underwent examination for HCV infection at our institute between 1990 and 2008 were recruited for this study. Patients with HCV infection at presentation were included, but patients with complications such as underlying lymphoproliferative disorders, autoimmune diseases like lupus nephritis, infection, and liver disease due to hepatitis B virus or alcohol abuse were excluded. A total of 35 patients were enrolled and they were divided into two groups according to the presence/absence of circulating cryoglobulins (cryo). The 23 patients who had cryo-negative and HCV-negative idiopathic MPGN were divided into subgroups with type 1 and type 3 disease.
Results: In the cryo-positive group (n = 9), 7 patients were positive for HCV infection, while 2 patients were negative. In the cryo-negative group (n = 26), 3 patients were positive for HCV infection, while 23 patients were negative (idiopathic MPGN). Compared with the cryo-negative group, the cryo-positive group had several characteristics such as more severe thrombocytopenia, higher serum immunoglobulin (Ig)G and IgM levels, lower levels of hemolytic complement (CH50) and complement component (C)4, predominant IgM staining, and type 1 histology. Patients with cryo-negative and HCV-negative 'idiopathic' MPGN showed predominant staining for IgG in both type 1 and type 3 cases, unlike the predominant staining for IgM in the cryo-positive group. Compared with type 3 cases, type 1 cases had a younger age, lower levels of CH50, C3 and C4, and less proteinuria. In the cryo-positive group, 4 patients (44.4 %) died, with death from B cell lymphoma and liver failure in 2 patients each, while 1 patient (8 %) developed end-stage renal failure requiring dialysis. In contrast, all patients in the cryo-negative group remained alive during follow-up, although 4 patients (2 type 1 cases and 2 type 3 cases) required dialysis.
Conclusion: Cryo-positive MPGN shows a close relationship with HCV infection and IgM, resulting in a poor prognosis. Cryo-negative and HCV-negative idiopathic MPGN has a close relationship with IgG staining, and type 1 cases feature characteristics such as a younger age, more severe hypocomplementemia, and less proteinuria than in type 3 cases.