Update on IgM Nephropathy

Abstract

IgM nephropathy (IgMN) is a relatively recently described, and still a controversial clinicoimmunopathologic entity which presents mainly as idiopathic nephrotic syndrome (INS) in both children and adults (Al-Eisa et al., 1996). The disease, like IgA nephropathy (IgAN), is defined by its immunohistologic features: the presence of immunoglobulin M (IgM) as the sole or dominant immunoglobulin in the mesangium of the glomeruli in a diffuse (all glomeruli) and global (whole glomerulus) distribution (Bhasin et al., 1978; Cohen et al., 1978). Similar to IgAN, the light microscopic (LM) features on renal biopsy are very heterogeneous, ranging from minimal change lesion to variable degree of mesangial proliferation to focal segmental glomerulosclerosis (FSGS) (Mubarak et al., 2010). Electrondense deposits in the mesangium are a variable ultrastructural feature. Its epidemiology is interesting; the disease is reported mostly from South East Asia and Eastern Europe, but sparse studies have also appeared from USA, Canada, and parts of Western Europe. Its etiology and pathogenesis are still not well understood (Myllimaki et al., 2003). Owing chiefly to controversy over its distinct nature, it has attracted little interest in the scientific community. There are very few studies on the prognostic factors (Jungthirapanich et al., 1997; Myllimaki et al., 2003). Currently, IgMN is treated along the similar lines as minimal change disease (MCD) or FSGS, but the response to steroids is less favorable than that of MCD. Its prognosis is relatively guarded as compared with MCD. Upto one third of individuals with IgMN develop renal insufficiency or one fourth, the end-stage renal disease (ESRD) over 15 years of follow-up (Myllimaki et al., 2003). In this chapter, we briefly discuss the historical background, etiology, pathogenesis, pathology, clinical manifestations, treatment, and prognosis of this relatively young and still largely controversial primary glomerulopathy. Further long term longitudinal studies are needed to clarify the status of the disease among the primary glomerulopathies.