Increasing incidence of focal-segmental glomerulosclerosis among adult nephropathies: A 20-year renal biopsy study

Abstract

Studies and textbooks from the 1970s and early 1980s list focal-segmental glomerulosclerosis (FSGS) as accounting for 10% to 15% of cases of idiopathic nephrotic syndrome in adults, although a recent review by D'Agati (Kidney Int 46:1223–1241, 1994) reported an approximately sevenfold increase in the incidence of FSGS from 1974 to 1993 in an active renal biopsy practice. To investigate possible changes in the incidence of FSGS in our renal biopsy practice, we reviewed reports from all nontransplant, adult (≥ 18 years) renal biopsies received in our laboratory from 1974 to 1993, which comprised 7,420 cases. All diagnoses of membranous nephropathy (MN), minimal change nephropathy (MCN), and FSGS made in each year were compiled; cases clearly or suspicious of being secondary to an underlying systemic disease, glomerulonephritis, or drug reaction were excluded. Relative frequencies of MN, MCN, and FSGS among these three diseases and among all biopsies were calculated for each year of the study. Regression analysis showed a significant (P < 0.001) increase in the odds of a diagnosis of FSGS over the study period: 7.6% per year among all biopsies and 6.8% per year among cases of MN, MCN, and FSGS only. Among all biopsies, the yearly incidence of FSGS increased from 4.0% ± 0.6% (mean ± SD) during the period between 1974 and 1979 to 12.2% ± 2.0% during the period from 1987 to 1993. The odds of a diagnosis of MN (mean yearly incidence, 9.5% ± 1.9%) did not vary significantly over the study period while the odds of a diagnosis of MCN (mean yearly incidence, 4.0% ± 1.2%) declined at a rate of 2.2% per year (P < 0.03). Frequencies of diagnosis of MN, MCN, and FSGS by two pathologists were almost identical. Review of available slides from cases of FSGS revealed 21 (none before 1980) with characteristic histologic features of the collapsing glomerulopathy (CG) variant of FSGS. No more than four cases of CG were observed in any year of the study, and CG accounted for 4.7% of total FSGS cases for which diagnostic slides were available. Compared with 42 patients with non-CG FSGS, the CG cohort showed a greater percentage of black patients (86% v 38%), significantly higher mean levels of serum creatinine (3.8 ± 2.7 mg/dL v 1.9 ± 1.5 mg/dL) and urinary protein (14.3 ± 9.6 g/24 hr v 7.7 ± 5.8 g/24 hr) at the time of renal biopsy, and a greater likelihood of and more rapid progression to end-stage renal failure. Our findings confirm an increase in the incidence of FSGS over the 20 years between 1974 and 1993, both overall and among primary nephropathies leading to the nephrotic syndrome. In agreement with others, we find that CG appears to represent a particularly “malignant” variant of FSGS, although in our experience this variant is observed relatively infrequently.