Background It is often difficult to classify small vessel vasculitis, especially AAV, as Granulomatosis polyangitis [GPA], Microscopic polyangitis [MPA], Eosinophilic granulomatosis polyangitis [EGPA] & Idiopathic cresentic glomerulonephritis. But with the discovery of ANCA, rheumatologists divide this as ANCA positive or negative vasculitis.

Objectives To classify AAV as anti-proteinase 3 (PR3) antibody+ or anti-myeloperoxidase (MPO) antibody + & compare their clinical presentation & outcome.

Methods 49 patients were included in our study from August 2011 till January 2017. Patients were classified according to PR3 and MPO serology [based on ELISA].

Results Median follow up was 18 months. PR3 + were 38 and 11 patients were MPO+. GPA was significantly higher in PR3 Group vs MPO group [36 (94.7%) vs 1 (9.1%) p<0.0001*] while MPA was significantly lower in PR3 group as compared to MPO (2 [5.3%] vs 5 [45.45%] p=0.001*). All EGPAs were MP0+ (4 [36.35%]). 48 fulfilled ACR clinical criteria for GPA/MPA or EGPA. 1 patient with arteritic anterior ischemic optic neuropathy without any other major organ involvement had significantly higher titres of MPO antibodies & was sorted as unclassified AAV. None were idiopathic crescentic glomerulonephritis in our cohort. 18 were biopsy proven [15 PR3+vs 3 MPO+]. Lung involvement was significantly higher in PR3 group than MPO group (32 [84.2%] vs 6 [54.5%] p=0.037*).Kidney involvement was also more in PR3 group but was not statistically significant (20 [52.6%] vs 4 [36.4%] p=0.341). Upper respiratory involvement was significantly higher in PR3 group (26 [68.4%] vs 3 [27.3%] p=0.014*).

Comparision between manifestations of ophthalmic, cardiac, peripheral vascular system & nervous systems of PR3+ & MPO+ groups was not statistically significant.

Complete remission without permanent organ damage was seen in 16 (42%) vs 6 (54.5%) in PR3 and MPO groups respectively (p=0.465). Frequency of relapse/refractory disease, though higher in PR3 group, was not statistically significant (PR3 vs MPO, 10 [26.3%] vs 1 [9.1%] p=0.228). Rates of morbidity & mortality were not significant statistically between PR3 & MPO groups (11 [28.9%] vs 2 [18.2%] p=0.476 & 3 [7.9%] vs 1 [9.1%] p=0.899 respectively). Similar comparisons were made between those who were classified clinically as GPA, MPA & EGPA with respect to remission, relapse, morbidity and mortality. All EGPAs achieved remission. Comparison between groups when divided as GPA & PR3 and MPA & MPO did not show statistical significance. 15 patients (all clinically GPA & PR3+) of the cohort [39.5%] received rituximab for relapse/refractory disease during/after initial induction therapy with cyclophosphamide & steroids.

Conclusions In this study, we did not find any advantage of clinical classification over serological. Wrongly diagnosing patients when disease is still evolving & inter-clinician bias are eliminated when classifying patients according to serology. Classification as PR3 & MPO is simpler and universal.

References

1. Hunder, G. G. et al. The American College of Rheumatology 1990 criteria for the classification of vasculitis. Introduction. Arthritis Rheum. 33,1065–1067 (1990).

2. Houben E, Bax WA, van Dam B, et al.Diagnosing ANCA-associated vasculitis in ANCA positive patients: A retrospective analysis on the role of clinical symptoms and the ANCA titre. Carubbi. F, ed. Medicine. 2016;95(40):e5096.

References

Disclosure of Interest None declared