INCIDENCE OF BIOPSY-PROVEN PRIMARY GLOMERULONEPHRITIS IN AN ITALIAN PROVINCE

Between January 1, 1970, and December 31, 1994, 1,926 cases of biopsy- proven primary glomerulonephritis (PGN) were diagnosed in an adult pop ulation (>15 years of age) in a northwestern region of Italy with appr oximately 3.5 million inhabitants. The principal long-term changes wer e an increase in the absolute number of biopsies per year, an increase in the mean age of patients undergoing biopsy (from 29.3 +/- 12.2 yea rs to 47.0 +/- 17.8 years), an increase in the percentage of patients older than 65 years (from 1.7% to 20.4%), and an increase in the perce ntage of isolated urinary abnormalities as an indication for biopsy (f rom 3.5% to 29.6%). In the total biopsy material, immunoglobulin A glo merulonephritis (IgA-GN) is the most frequent type (26%), followed by membranous glomerulonephritis (MGN; 20%). An incidence study was begun in 1990; this survey was restricted to the population of the province of Torino (approximately 2 million inhabitants) as only this area com pletely refers to the nephrologic centers that entered patients into t his study. The overall incidence of PGN is 4.68 new cases/yr/10(5) pop ulation with a predominance of males (>2:1); IgA-GN is the most common type (1.47/yr/10(5) population [34.5%]) in the overall population. In the elderly, cases of PGN are twice as high as in adults (8.19/yr/10( 5) population v 4.02/yr/10(5) population in the 65 to 74 year and 45 t o 54 year age groups, respectively); MGN mainly accounts for this high incidence (3.4/yr/10(5) population), while the nephrotic syndrome is the most common indication for biopsy (53.8%). A comparison with the i ncidence in the same area in the early 1970s is evaluable only for PGN , which was mainly registered in the age groups for which an unrestric ted biopsy policy was already in place (15 to 35 years). In contrast w ith a misleading increase of all types of PGN, which is in reality due to the extension of the biopsy policy to older and asymptomatic patie nts, membranoproliferative glomerulonephritis type I shows a countercu rrent decrease from 0.43 to 0.13/yr/10(5) population. Evidence of a si multaneous decrease in severe cardiac valvulopathy, due to rheumatic f ever, is also provided. We feel that before epidemiologic conclusions can be reached, a clear understanding of one's own biopsy policy is es sential. An apparent change in the PGN rate in our region over the las t 25 years mainly depends on modifications in our biopsy policy, most probably coupled with a change in the threshold of detection of sympto ms in the general population. At present, according to our experience, IgA-GN is the most common type of PGN in the total bioptic material, as demonstrated in other European countries, while the elderly show a peculiar pattern with a higher PGN incidence, mainly represented by MG N and heralded by the nephrotic syndrome. We also confirm that membran oproliferative glomerulonephritis type I is indeed decreasing in paral lel with changes in the microbiologic environment. (C) 1996 by the Nat ional Kidney Foundation, Inc.