Kidney Biopsy Chronicity Grading in Antineutrophil Cytoplasmic Antibody Associated Vasculitis.

BACKGROUND Kidney biopsy is valuable for prognostic assessment of renal outcomes in antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) with glomerulonephritis (AAV-GN) but the impact of chronic changes is not determined. METHODS A retrospective cohort study of MPO- or PR3-ANCA positive patients with AAV and active renal disease. We applied the Mayo Clinic Chronicity Score (MCCS), validated and evaluated its implications on outcome prediction in AAV-GN. RESULTS We analyzed 329 patients with kidney biopsies available to score. The extent of chronicity was graded by MCCS as (i) minimal - 102 (31.0%), (ii) mild - 106 (32.2%), (iii) moderate - 86 (26.1%), and (iv) severe - 35 (10.6%). The MCCS grades correlated with the degree of renal function impairment at presentation (mean eGFR: 48.3 vs. 29.2 vs. 23.7 vs. 18.5 mL/min/1.73 m2, p < 0.0001). Higher degrees of the individual components of the MCCS (glomerulosclerosis, interstitial fibrosis, tubular atrophy and arteriosclerosis) were associated with lower median eGFR (p < 0.0001) and decreased event free (kidney failure (KF) and death) survival (p = 0.002, p < 0.0001, p < 0.0001 and p = 0.017, respectively). Patients with lower MCCS grades recovered renal function more frequently (p < 0.0001). Increasing MCCS grades were associated with decreased renal recovery (p = 0.001), more frequent events and shorter time to KF (p < 0.0001), KF and death (p < 0.0001), and death (p = 0.042), independently of remission-induction treatment used (CYC or RTX). The MCCS stratified renal outcomes for each MCCS grade and can be used in clinical practice as a cut-off for KF prediction (MCCS≥4). CONCLUSIONS Chronic changes on kidney histology independently predict renal function, outcomes and response to treatment in AAV-GN.