Total cortical interstitial inflammation predicts chronic kidney disease progression in patients with lupus nephritis

End-stage kidney disease (ESKD) from lupus nephritis (LN) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Kidney biopsy is the gold standard for diagnosis and prognostication of LN. While interstitial fibrosis and tubular atrophy (IFTA) predict progression to ESKD, the National Institutes of Health (NIH) classification of interstitial inflammation in unscarred cortical parenchyma is not predictive of chronic kidney disease (CKD) progression. The objective of this study was to determine whether total cortical interstitial inflammation that accounts for inflammation in the entire cortical parenchyma could predict CKD progression in patients with LN. Early identification of at-risk patients may improve outcomes.This retrospective cohort study included 125 SLE patients with LN class III, IV, V or mixed (III/V, IV/V) on the index biopsy (2005-2018). Kidney biopsies were reviewed and assigned based on the 2018 NIH Activity Index (AI) and tubulointerstitial lesion categories. Total interstitial inflammation in the entire cortical parenchyma was graded as 0, 1, 2 or 3, corresponding to <10%, 10-25%, 26-50% and >50%, respectively, of the total cortical parenchyma containing an inflammatory infiltrate (similar to the definition used in the Banff total inflammation score). CKD progression was defined as an estimated glomerular filtration rate decrease of ≥30% within 5 years after the index biopsy. Kaplan-Meier survival curves and Cox proportional hazards models were performed to compare the two scoring systems, the total cortical intestinal inflammation score and the NIH interstitial inflammation score as predictors of CKD progression.Of 125 patients, 46 experienced CKD progression; 21 of 46 subsequently developed ESKD, 28 (22.4%) had moderate-severe total cortical interstitial inflammation and 8 (6.4%) had moderate-severe NIH interstitial inflammation. There were no differences in baseline characteristics between progressors and nonprogressors. Total cortical interstitial inflammation was associated with CKD progression in time-dependent analyses [hazard ratio 2.45 (95% confidence interval 1.2-4.97)] adjusted for age at biopsy, race, sex, LN class and hypertensive vascular change on kidney biopsy. The NIH interstitial inflammation was not associated with CKD progression.In contrast to the current NIH interstitial inflammation classification, accounting for interstitial inflammation in the entire cortical parenchyma allows identification of patients at risk for CKD progression in LN.