Changing Incidence of Glomerular Disease in Olmsted County, Minnesota

Membranous nephropathy (MN) is considered the most common cause of nephrotic syndrome in white adults, but recent studies have shown an increasing incidence of focal segmental glomerulosclerosis (FSGS). These studies are difficult to interpret because the majority of cases came from urban tertiary referral centers. For validating these findings in the general population, trends in the incidence of various forms of glomerular disease (glomerulonephritis GN) among the residents of Olmsted County, MN were studied. Biopsy data of local patients who had a diagnosis of a nondiabetic glomerular disease from 1974 through 2003 were reviewed. Biopsies were categorized as (1) FSGS, (2) MN, (3) minimal change, (4) lupus nephritis, (5) membranoproliferative GN (MPGN), (6) IgA nephropathy (IgAN), (7) crescentic/necrotizing GN, and (8) other. Time trends in the annual age- and gender-adjusted (2000 US population) incidence rate per 100,000 Olmsted County population were estimated. A total of 195 biopsies were analyzed. Overall, IgAN was present in 22%, FSGS was present in 17%, and MN was present in 10%. Between 1974 to 1983 and 1994 to 2003, the incidence of any type of GN among Olmsted County residents increased more than two-fold (P < 0.001), FSGS by 13-fold (P < 0.001), and IgAN by three-fold (P = 0.002). Increases in MN were nonsignificant (2.5-fold; P = 0.13). Currently (1994 to 2003), the most frequent type of GN is IgAN (25%), followed by FSGS (20%) and MN (11%), with annual incidence rates of 2.1, 1.8, and 1.0 per 100,000/yr, respectively. This study confirms that the incidence of GN is growing overall, particularly for FSGS, which is the leading cause of nephrotic syndrome in white adults.