#4683 CHARACTERISTICS AND OUTCOMES OF MPO VERSUS PR3 ANCA ASSOCIATED GLOMERULONEPHRITIS: A REPORT FROM AN AUSTRALIAN POPULATION-BASED STUDY
Authors: Chau Ken , Ng Shu Kay , Lam Alfred , Khoo Tien , Ranganathan Dwarakanathan 
Published: June 2023

Abstract

Background and Aims
ANCA-associated vasculitis is a group of autoimmune vasculitides of unknown aetiology that predominantly affect small blood vessels among different organ systems, with different phenotypic manifestations. Myeloperoxidase (MPO) and Proteinase 3 (PR3) have emerged as two main serological subtypes and growing evidence has shown there are differences between their disease characteristics [1,2]. We investigate into the difference in histological presentation, disease manifestation and progression, as well as mortality rate in patients with biopsy confirmed ANCA associated glomerulonephritis (AAGN).

Method
This retrospective study was performed at the Royal Brisbane and Women's Hospital, a major tertiary hospital that service a population of 1,030,006 in North Brisbane, Australia. The 2012 Chapel Hill Consensus Conference definitions was used to identify renal predominant ANCA vasculitis. Patients with pauci-immune glomerulonephritis confirmed on kidney biopsy between 1st January 2005 to 1st October 2021 were selected for review. Biopsies were categorised according to Berden's histopathologic classification. Clinical data were collected via medical records.

Results
Of 80 cases of AAGN identified during the study period, 53 cases were MPO/pANCA positive and 21 cases were PR3/cANCA positive, there were 5 ANCA negative cases and one indeterminate case due to unavailable serology results. There was no statistical significant difference between gender and ANCA subtype (Male MPO 53% and Male PR3 48%, p=0.57). Lung involvement was the most common extra-renal manifestation of AAGN. Similar rates were found between MPO and PR3 positive diseases, 30% (16/53) and 29% (6/21), respectively. PR3 AAGN were much more likely to have sinus involvement, 14% (3/21) vs 4% (2/53) (Relative Risk 3.8, p=0.13). Berden classification was used to classify renal biopsy results (Table 1). There were more cases of sclerotic AAGN within the MPO group whereas crescentic AAGN cases were more common in the PR3 group (Fisher Exact test, p=0.43) Estimated Glomerular Filtration Rate (eGFR) were measured at time of AAGN diagnosis compared to at 3 years. In the MPO group, 45% cases had recovery of eGFR by at least 5mls/min, compared to 62% in PR3 group (P = .30). In addition, 91% (40/44) had improvement of MPO titre following induction treatment, compared to 83% (15/18) in PR3 group had improvement in their titre (p=0.40). Eighteen percent (14/80) of AAGN cases died during the study period. The crude mortality rate for MPO, PR3 and ANCA negative cases were 21% (11/53), 10% (2/21) and 20% (1/5) respectively (p=0.33).

Conclusion
In our cohort, MPO AAGN was more prevalent (RR 2.5), more likely to have sclerotic class on biopsy (i.e. typically carries the worst prognosis), less likely to have eGFR recovery following treatment and had a higher mortality rate. This is despite the MPO group having a higher titre response rate. Both MPO and PR3 are associated with lung involvement but sinus involvement was significantly more common in PR3 disease. ANCA negative pauci-immune GN remains an uncommon, recognised subtype. Allowing for rarity of disease, larger longitudinal cohort studies are desirable to further define the disease characteristics between AAGN subtypes.