BACKGROUND: Immunoglobulin M (IgM) nephropathy (IgMN) is characterized by the IgM deposition in the kidney's mesangium. We assessed the impact of electron-dense deposits (EDDs) on IgMN and compared it to other kidney diseases. METHODS: We enrolled 63 adult patients with IgMN who underwent renal biopsy from May 2003 to June 2017. We compared clinicopathological features of IgMN based on EDD presence
compared characteristics to 91 minimal change disease (MCD), 103 focal segmental glomerulosclerosis (FSGS), and 469 immunoglobulin A nephropathy (IgAN) patients. Renal events were defined as a >
50% decrease in estimated glomerular filtration rate (eGFR), eGFR of <
15 mL/min/1.73 m2, or end-stage renal disease development. RESULTS: IgMN patients with EDDs had increased mesangial cellularity, matrix accumulation, prominent immunofluorescent staining, and more diffuse podocyte effacement than those without EDD. Clinical characteristics and renal outcomes did not differ significantly based on EDD presence. During 79.5 ± 58.8 months of follow-up, renal events developed in 46.2% and 46.0% of IgMN cases with and without EDD. IgMN (46.0%) and FSGS cases (40.8%) had similar frequencies of renal events and higher frequency than MCD (18.7%) or IgAN cases (26.4%). IgMN cases had more severe manifestations than MCD and IgAN
higher blood pressure, lower proteinuria, and eGFR levels at biopsy than MCD cases
higher blood pressure, proteinuria, frequency of acute kidney injury, and lower eGFR levels. CONCLUSION: Clinical characteristics of IgMN did not differ based on EDD presence. Therefore, IgMN should be defined based on IF findings. IgMN shared clinical characteristics with FSGS but had more severe than MCD and IgAN.