Incidence and Proportion of Primary Focal Segmental Glomerulosclerosis (FSGS) among a Racially and Ethnically Diverse Adult Patient Population between 2010-2021

Background: Focal segmental glomerulosclerosis (FSGS) refers to a pattern of glomerular injury but also includes primary FSGS which is considered as an immune mediated glomerulopathy. We sought to determine the incidence of primary FSGS and proportion of FSGS patients with primary FSGS among a large diverse patient population in the United States. Methods: A cross-sectional study (2010-2021) was performed within an integrated health system in patients (age ≥18yrs) with biopsy-proven FSGS. Among biopsies with FSGS as the first diagnosis on pathology report, chart reviews were performed to determine primary FSGS, defined as podocyte foot process effacement ≥80% on electron microscopy. The proportion of patients with primary FSGS and annual incidence rates (per 100,000 patient-years) were calculated. Standardized incidence rates were determined by age, sex, and race and ethnicity based on US population structure of the five-year (2018-2022) American Community Survey estimates. Results: We identified 3,838 patients with FSGS reported on biopsy. Among 1,502 with FSGS as the principal diagnosis, 637 met criteria for primary FSGS (mean [SD] age 55.5 years [17.9], 56.5% male, 35.6% Hispanic, 28.7% White, 17.9% Asian/Pacific Islander, and 16.0% Black). The mean standardized incidence rate [CI] of primary FSGS was 1.7 [0.9, 2.5] per 100,000 patient-years during the study period. The standardized annual incidence rates ranged from 1.3 – 2.4 per 100,000 patient-years. Incidence rates (per 100,000 patient-years) were highest among Black (3.2), Asian (2.7), and Pacific Islander (2.8) patients. Conclusion: Primary FSGS accounted for 16.6% of biopsy-proven FSGS. Primary FSGS is a likely a rare disease with incidence highest among Black, Asian, and Pacific Islander people. More precise identification of primary FSGS may facilitate work to improve understanding of this glomerulopathy and improve kidney outcomes.