#6407 RENAL LIMITED VASCULITIS: DATA FROM A CROATION REFERRAL CENTER
Authors: Crnogorac Matija , Kacinari Patricia , Toric Luka , Kasumović Dino , Zivic Ana , Tišljar Miroslav , Ljubanović Danica Galešić , Galesic Kresimir , Horvatic Ivica 
Published: June 2023

Abstract

Background and Aims
Small vessel vasculitis and in particular ANCA associated vasculitis (AAV) are diseases with variable clinical presentation. Renal limited vasculitis (RLV) can vary in presentation and characteristics compared to systemic disease. There is a tendency to categorise RLV as a part of microscopic polyangiitis (MPA) spectrum though there seem to be differences in terms of both histology and serology between RLV and MPA. We present data on patients with renal limited vasculitis from our referral center.

Method
This study included 106 consecutive AAV patients with biopsy proven renal involvement in the period from 2007-2017. Category variables were analysed with Fisher Exact testom and continuous with Kruskal-Wallis testom. Statistical difference was then analysed posthoc with Chi-square test. Kaplan Meyer survival analysis and multivariate Cox proportional hazard regression analysis were used to explore difference between clinical phenotypes and finding significant predictors regarding outcomes which were defined as combined outcome end-stage renal disease and death (ESRDD), ESRD alone, the death outcome alone and relapse rate.

Results
Out of 106 AAV patients with renal involvement in our database: 66 (61,1%) MPA, 20 (18,5%) GPA (granulomatosis with polyangiitis), 20 (18,5%) RLV. In RLV group 14 (70%) were female and average age was 55 (IQR 47-60). Average SCr in RLV group was 234 μmol/l (IQR 168-376,5) and median proteinuria was 3,3g/24h (IQR 0,9-3,8) and most of these patients presented with either nephrotic syndrome (30%) or RPGN (30%). Serologicaly 90% of RLV patients were ANCA negative and 10% were MPO-ANCA positive. Histologicaly (Berden classification) 60% had mixed class, 25% crescentic, 10% focal and 1% sclerotic. Average BVAS score was 14 (IQR 12-17). Compared to MPA and GPA, RLV patients were younger (p=0,058), had less expressed constitutional symptoms (p= 0,013) with lower average BVAS (p=0,0001) and lower CRP levels (p=0,001). Though there was no significant difference of average SCr level RLV patients presented more often with nephrotic syndrome (p=0,014), had histological predominantly mixed class (p=0,006) and higher interstitial fibrosis and tubular atrophy (IFTA) percentage (p=0,086). Interestingly, compared to MPA and GPA majority of RLV patients were ANCA negative (p=0,001). There were no statistically significant differences in treatment used both in induction (including need for dialysis and/or PLEX) or remission maintenance treatment between RLV, MPO and GPA group. In survival analysis there was no statistical differences for all of the outcomes between RLV group, MPA and GPA group.

Conclusion
RLV can be challenging disease considering it's clinical presentation but also characteristics of renal involvement in terms of more often nephrotic proteinuria and higher IFTA percentage. This might suggest that these patients could have slower disease course (so called slower progressors). Also interestingly in our cohort most of these patients were ANCA negative which also makes diagnosis predominantly a combination of clinical presentation and histology thus prompting a question of how should we classify RLV within a spectrum of small vessel vasculitis. More research is needed to better understand the RLV.