Classifying ANCA-Associated Vasculitis and Correlating Outcomes Based on Anti-PR3/MPO Serology

Abstract

Introduction: Diagnosis and management of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a challenge for all. Overlapping features in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) make diagnosis sometimes difficult. We aimed to classify clinical features and outcomes of proven AAV according to their serology, viz., anti-PR3/myeloperoxidase (MPO) by the enzyme-linked immunosorbent assay (ELISA). Materials and Methods: This was a prospective observational study of a total of 66 patients. This study included all consequent (old and new) AAV patients visiting a tertiary care center in northern India from August 2012 to June 2018. Patients were followed up for a minimum of 6 months. ANCA was done by both immunofluorescence assay and ELISA. Results and Conclusion: When compared, serological classification yielded findings similar to clinical counterparts [PR3/MPO vs. GPA/MPA]. The majority [80.3%] of patients were PR3-positive and were GPA clinically. Lung involvement was common in the PR3 group; however, there was no significant difference between the two groups [viz., PR3 and MPO, P = 0.18]. ENT involvement was significantly higher in the PR3 group when compared with the MPO group [P-value=0.009]. The difference in renal involvement in both the groups was not significant [P = 0.28]. Renal biopsy findings were similar in both the PR3/MPO groups. The median follow-up period was 18 vs. 12 months in the PR3 and MPO groups, respectively. Relapse was significantly higher in the PR3 group [P = 0.017]. The PR3 group significantly required rituximab for second induction treatment [P = 0.028]. Eight patients (12.12%) died during the study period. There was no significant difference in mortality, and there was permanent organ damage in both the PR3 and MPO groups. Autoantibody-based classification is supplemental to the clinical segregation of AAV phenotypes.