Glomerulopathy with mesangial IgM deposits: long-term follow up of 64 children.

BACKGROUND

The aim of the present study was to investigate to what extent IgM nephropathy in children with minimal change nephrotic syndrome (MCNS) and diffuse mesangial hypercellularity (DMH) evolves to focal segmental glomerulosclerosis (FSGS).

METHODS

Tissues from renal biopsies were examined by light microscopy (LM), immunofluorescence (IF) and, in four cases, by electron microscopy (EM). From a total of 352 nephrotic children, 121 had renal biopsy results as steroid dependent or resistant. A diagnostic renal biopsy was also performed in 331 children with non-nephrotic proteinuria and/or hematuria. A second renal biopsy was performed in 16 children whose renal function was impaired during the follow up. The clinical course of IgM-positive children was compared with that of IgM-negative children.

RESULTS

Of the 121 nephrotic children with renal biopsy, 85 were MCNS. Twenty were IF positive mainly for IgM, six of whom (30%) presented evolution to FSGS, while of the remaining 65 IF-negative children, only three (4.6%) presented evolution to FSGS. Of the total 331 children with non-nephrotic proteinuria and/or hematuria, 139 were diagnosed as IgA--IgG nephropathy, 44 had positive IF for IgM and 148 were IF negative. Of the 44 children IF positive for IgM, seven (15.9%) presented evolution to FSGS, while none of the 148 IF-negative children presented evolution to FSGS. The follow-up time for all children ranged from 1 to 14 years.

CONCLUSIONS

Of IgM nephropathy patients with MCNS and DMH, a significant percentage develop impaired renal function, due to the evolution of FSGS, as revealed by repeat biopsy during long-term follow up.