Clinical significance of IgM and C1q deposition in the mesangium in pediatric idiopathic nephrotic syndrome

Abstract

In biopsy-proven idiopathic nephrotic syndrome (INS), immunoglobulin M (IgM) and C1q are occasionally deposited in the mesangium. In pediatric nephrology, the significance of mesangial IgM or C1q deposits is controversial, based on previous reports. The aim of this study was to explore the clinical significance of mesangial IgM and/or C1q deposits in pediatric INS patients, especially the initial responses to steroids and final outcomes. We reviewed the clinical courses of 70 children with steroid-dependent or steroid-resistant INS who underwent a renal biopsy at our hospital from 1998 to 2010. There were 30 mesangial IgM immunofluorescence (IF)-positive (IgM+) children. The IgM+ group was compared with the IgM IF-negative (IgM-) group. In addition, we reviewed the clinical characteristics of 8 mesangial C1q IF-positive (C1q+) children. Of the 30 IgM+ children, 10 (33.3%) were steroid-dependent (IgM- group: 18/40, 45%) and 14 (46.7%) were steroid-resistant (IgM- group: 11/40, 27.5%; p<0.05). Although a high frequency of steroid-resistant INS was observed in the IgM+ group, the efficacy of cyclosporine (CyA) therapy was relatively good (all 14 steroid-resistant children obtained complete or partial remission). Moreover, all 8 C1q+ children obtained complete remission after CyA therapy, although they had a high frequency of steroid resistance (7/8, 87.5%), and 1 child was steroid-dependent. Our results indicate that, regardless of the histological pattern (minimal change disease, focal segmental glomerulosclerosis or diffuse mesangial hypercellularity), children with IgM+ and/or C1q+ INS have good responses to CyA. IgM+ and/or C1q+ may be markers of the initial disease severity of INS.