LAUSR

In 2010 a new histopatological classification for ANCA-associated GN (ANCA GN) was developed – the Berden classification. It is composed of four categories – focal, crescentic, sclerotic and mixed - based on the predominance (≥50%) of normal glomeruli, cellular crescents, and globally sclerotic glomeruli, respectively. The mixed category, related to an intermediate renal outcome, has no glomerular feature predominating. Our aim was to evaluate other histopathological characteristics that could be significant in the mixed group and their impact on survival and renal outcome. This is a multi-center retrospective observational study which included patients with ANCA GN who were submitted to kidney biopsy at the time of clinical diagnosis, between 2013 and 2018. Several histopathological data were analysed, including percentage of cellular, fibrocellular and fibrous crescents; presence of fibrinoid necrosis, interstitial hemorrhage, tubular atrophy ant interstitial fibrosis. Clinical data such as need of dialysis at presentation and death, during a 2 year follow up period, were also examined. The patients were classified accordingly to the histopathological Berden classification. For statistical analysis purposes they were divided in two groups: mixed and non-mixed. Categorical variables are presented as frequencies and percentages, continuous variables as means and standard deviations, or medians and interquartile ranges (IQR) for variables with skewed distributions. Statistical analysis was performed using SPSS version 25 for Windows. We observed 51 ANCA GN kidney biopsies: 68.5% (n=35) from mixed, 11.8% (n=6) from crescentic and sclerotic and 7.8% (n=4) from focal category. In average, the biopsies contained 10.4±4.8 glomeruli. The percentage of fibrous crescents was significantly higher in mixed than non-mixed group (16.1±18.6% vs 7.2±17.9%; p=0.037). Although not statistically significant, the percentage of fibrocellular crescents was higher (10.3±20.9 vs 6.2±12.5; p=0.512) and the percentage of cellular crescents was lower (15.4±18.2 vs 34.3±37.7; p=0.072) in mixed group. The presence of fibrinoid necrosis (54.3% vs 87.5%; p=0.021) and fibrinoid necrosis with cellular crescents (34.3% vs 68.8%; p=0.022) were both lower in mixed category. There was no difference in the need of dialysis at presentation between both groups, but the percentage of fibrous crescents was a predictor of dialysis induction at admission in all cases [p=0.009; adjusted odds ratio (OR) 1.053 (CI: 1.013–1.096)]. Deaths were significantly higher in mixed group (34.3% vs 6.3%; p=0.033). There are other morphological aspects that seem to be relevant in the characterization of different histological classes of ANCA GN. Having more chronic lesions, like the percentage of fibrous crescents, and a less frequency of acute lesions, such as fibrinoid necrosis, proved to be relevant in the mixed group and may be associated to the higher mortality in this class. Besides, the percentage of fibrous crescents was itself a predictor of the need of dialysis, which highlights the importance of assess other characteristics, in addition to those included in the current ANCA GN classification. However, further studies and larger samples are needed to evaluate better the importance of other morphological features in this classification and their influence on survival and renal outcome of these patients.