Progressively Decreasing Incidence of Membranoproliferative Glomerulonephritis in Spanish Adult Population

Spanish Society of Nephrology, Hospital Ramón y Cajal, Carretera de Colmenar, Km. 9,100, E-28034 Madrid (Spain) Dear Sir, 35η Several recent reports have called attention to the progressively decreasing incidence of membranoproliferative glomerulonephritis (MPGN) in the last decade [1–7]. In order to test this observation, we reviewed 8,545 renal biopsies in adult patients with primary glomerulonephritis (GN) examined at 33 nephrology units in Spain from January 1970 to December 1986. The study was entirely retrospective. The diagnosis was established on the basis of a kidney biopsy studied by light microscopy and immunofluorescence. Patients less than 14 years of age were excluded. MPGN was classified as type I (subendothelial deposits) or type II (dense intram-embranous deposits). A variance analysis was made to test the ‘null hypothesis’, that is to say two variables are independent. A marked reduction in the annual incidence of MPGN, expressed as a percentage of the total number of GN, was observed after 1976 (fig. 1). Thus, we compared the mean annual incidence of the various types of GN during three periods: period I (1970–1976), period II (1977–1981) and period III (1982–1986). As shown in table 1, in spite of the increased total number of patients submitted to biopsy, the incidence of MPGN (26.4,14.7 and 11.9% for the three periods, respectively) was significantly lower for each of the periods when compared with the preceding period (p < 0.001 for periods I vs. II; p < O.Ol for II vs. III). This reduced incidence was observed only in patients with type I MPGN (table 2), whereas the incidence of type II MPGN and its contribution to the total number of patients with primary GN (1.8,1.9 and 2% for the three periods, respectively) did not significatively vary (data from 23 hospitals). In addition, except for idiopathic nephrotic syndrome whose frequency remained unchanged, we observed variations in the incidence of three other primary GN. The incidence of crescentic GN between period I (4.8%) and period III (7.3%; p < O.Ol), membranous nephropathy in period I (8.1%) versus period III (11.6%; p < 0.01) and IgA 30–25–20–15–10–5Year: 1970 -71 -72–73–74–75–76 -77–78–79–80–81 -82–83 -84–85–86 6–7–8-12–15–17–19– 23–27–27–32–33–33–33–33–33–33 Number of hospitals Fig. 1. Annual incidence of MPGN in the Spanish adult population expressed as the percentage of the total number of GN throughout the 17-year study period. nephropathy (10.9, 19.9 and 22.3% for the three periods, respectively, p < 0.01) was found to increase significantly with time (table 1). The incidence of crescentic GN in period III was similar to that of the Milan study [4] and the increased frequency has also been previously reported [3].