#2291 ANCA negative vasculitis—the unmet need within small vessel vasculitis
Authors: Crnogorac Matija , Floyd Lauren , Strizić Ana , Dhaygude Ajay , Kronbichler Andreas , Morris Adam , Galesic Kresimir , Horvatic Ivica 
Published: May 2024

Abstract

Background and Aims
ANCA negative small vessel vasculitis with renal involvement has been described in a number of cohorts. Though comprehensive studies comparing these individuals to ANCA positive patients are lacking and they are routinely excluded from clinical trials. Whilst the numbers are smaller than those with ANCA positivity, they still make up a large proportion of small vessel vasculitidies (Fig. 1). The absence of detectable circulating ANCA is thought to indicate a distinct spectrum of the disease. There remains unanswered questions regarding the pathophysiology, diagnosis and management of patients with seronegative AAGN. We present data from Croatian referral center.

Method
Study included 106 AAV patients with biopsy proven renal involvement in the period from 2007-2017. Category variables were analysed with Fisher Exact test and continuous with Kruskal-Wallis test. Statistical difference was then analysed post hoc 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
106 AAV patients with renal involvement were included: 66 (61.1%) MPA, 20 (18.5%) GPA, 20 (18.5%) RLV. 14 (13%) were PR3-ANCA positive, 57 (52.8%) MPO ANCA positive, 5 (4.6%) PR3-ANCA+MPO-ANCA and 32 (29.6%) ANCA negative patients. ANCA negative patients were comparatively younger (p = 0.02) and presented with more renal limited vasculitis (RLV; p &lt; 0.001), lower BVAS (p = 0.003) and lower CRP (p = 0.001). ANCA negative patients usually presented with nephrotic syndrome compared to positive ones which presented with rapid progressive nephritic syndrome or acute nephritic syndrome (p = 0.027). 24-hour proteinuria levels were higher in ANCA negative group (p = 0.003). Though statistical difference was not reached, there was tendency for ANCA negatives to receive less plasmapheresis (p = 0.074). Histologically there were no differences between ANCA positive and ANCA-negative patients. On sub analysis ANCA negatives versus individual seropositive groups, there was tendency that ANCA negatives and MPO-ANCA patients had lower percentage of glomerular crescents (p = 0.092) but more acute tubular damage (p = 0.087). There were no differences in clinical outcomes between the groups.

Conclusion
ANCA negative vasculitis form a large proportion of small vessel vasculitidies and present with different clinical laboratory and histological (renal) characteristics than ANCA positive ones. More often than not disease seems to be renal limited and patients tend to be younger. Due to the rarity of the disease, there remains unanswered questions regarding the pathophysiology, diagnosis and management of these patients. This study highlights noteworthy distinctions between the two groups. Whether these differences warrant adjustments in treatment algorithms or a reconsideration of the classification of small vessel vasculitis remains to be determined. Further investigation into the pathogenetic mechanisms of seronegative AAVs is essential.