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Year : 2022  |  Volume : 18  |  Issue : 3  |  Page : 73-79

Classifying ANCA-associated vasculitis and correlating outcomes based on anti-PR3/MPO serology: A prospective study from a tertiary care center

Division of Clinical Immunology & Rheumatology, Medanta The Medicity, Gurugram, Haryana, India

Date of Submission03-Apr-2022
Date of Acceptance12-May-2022
Date of Web Publication13-Dec-2022

Correspondence Address:
Dr. Gayatri G Ekbote
Deenanath Mangeshkar Hospital & Research, Deenanath Mangeshkar Hospital Road, Near Mhatre Bridge, Erandwane, Pune 411004, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/AMJM.AMJM_19_22

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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.

Keywords: ANCA, c-ANCA, MPO, p-ANCA, PR3, rituximab

How to cite this article:
Ekbote GG, Negalur N, Tanna D, Bindroo M, Raval D, Bajad S, Gupta R, Kazi W. Classifying ANCA-associated vasculitis and correlating outcomes based on anti-PR3/MPO serology: A prospective study from a tertiary care center. Amrita J Med 2022;18:73-9

How to cite this URL:
Ekbote GG, Negalur N, Tanna D, Bindroo M, Raval D, Bajad S, Gupta R, Kazi W. Classifying ANCA-associated vasculitis and correlating outcomes based on anti-PR3/MPO serology: A prospective study from a tertiary care center. Amrita J Med [serial online] 2022 [cited 2023 Mar 24];18:73-9. Available from: https://ajmonline.org.in/text.asp?2022/18/3/73/363497

  Introduction Top

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease characterized by inflammation of small- to medium-sized blood vessels.[1] ANCAs are antibodies directed against neutrophil enzymes, of which c-ANCAs are against proteinase 3 (PR3-ANCA) and p-ANCAs are against myeloperoxidase (MPO-ANCA).[2],[3] Clinically, granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA) are heterogeneous diseases that are distinguished by the involvement of different organ systems of variable severity, and most of them are characterized by a relapsing course. Among these, there is a distinct difference between EGPA and the other two, but there are overlapping features in GPA and MPA, making diagnosis sometimes difficult.

The Chapel Hill Consensus Conference (CHCC) criteria provided definitions of vasculitis.[1] These definitions are widely accepted in defining vasculitides by pathology, including the size of the affected vessels and the organ systems involved. In 1990, the American College of Rheumatology gave classification criteria for Wegener’s granulomatosis which is called as GPA now and for Churg–Strauss syndrome (now called as EGPA) but not for MPA.[4],[5]

The classification of ANCA-positive patients into only two classes depending on MPO and PR3 serology eliminates the clinician’s bias of classification into the traditional groups of GPA, MPA, and EGPA, at the same time, making classification easier.[6] Thus we performed a prospective analysis of AAV at our center and have tried to classify them on the basis of MPO and PR3.

  Materials and Methods Top

This was a prospective observational study carried out in the Department of Rheumatology at Medanta, The Medicity, Gurugram, Haryana, India. Patients were enrolled from August 2012 to December 2017. The last follow-up was completed up to June 2018. The inclusion criteria were patients with AAV, namely, GPA, MPA, and EGPA defined as per the CHCC 2012 criteria. Those patients who were already on follow-up at the beginning of the study, i.e., August 2012, were also included. The diagnosis of GPA, MPA, or EGPA was based on clinical manifestations, serology, imaging, and whenever feasible, a biopsy of the involved organ. As there were no patients of renal limited vasculitis, it was not considered. Demographic profile, clinical features, laboratory data, treatment details, disease activity, and therapeutic outcomes of patients were analyzed prospectively. Past medical records were reviewed and noted.

Organ manifestations were only registered if they could be ascribed to vasculitis. Assessment of the upper respiratory tract and ear nose throat (ENT) involvement was performed by examination, imaging, and audiometry, in collaboration with the ENT surgeon. Ophthalmic examination included slit-lamp examination and fundoscopy, which was performed by an ophthalmologist. Other systems were assessed by examination, laboratory tests, and imaging wherever needed.

The test for ANCA was performed by the indirect immunofluorescence (IIF) assay using the “Immunoconcept-ELISA” kit. At the same time, PR3 and MPO were tested by the line immunoassay (LIA). The LIA kit used was D-tek as per the standards used in our hospital. After the diagnosis was established as GPA or MPA or EGPA, they were re-classified on the basis of PR3 and MPO serology.

Disease activity was assessed as per the Birmingham Vasculitis Activity Score (BVAS). A higher score since first assessment was considered as persistent disease activity or active disease. The patient follow-up was monthly for 6 months, then 3 monthly or 6 monthly whichever was required as per the patient disease activity status. Disease outcomes were calculated based on the past medical records as well as from current records.

Informed consent from the patient was obtained before being enrolled in the study. The study protocol was approved by the Institutional Review Board of Medanta, The Medicity Hospital, Gurugram, Haryana, India. Data were analyzed using Statistical Package for Social Sciences (SPSS) version 24. Categorical data were compared using the χ2 test, whereas continuous data were analyzed using Student’s t-test. A P-value of less than 0.05 was considered significant, with 95% confidence interval for comparison of two proportions.

  Results Top

During the study period, there were 66 patients with AAV: 53 patients were GPA, 7 were MPA, 5 were EGPA, and 1 was unclassifiable. Constitutional symptoms were present in almost all patients. Musculoskeletal and skin manifestations were present in more than three-fourths of the patients. [Table 1] shows the baseline clinical features (organ involvement) in GPA, MPA, and EGPA. Tissue diagnosis was obtained in a total of 27 (40.9%) patients. Biopsies included 15 renal patients [PR3=8/MPO=7]. Also, six lung and two each of skin, GIT, and nasal tissues were there. All of them were PR3-positive and were clinically GPA.
Table 1: Organ involvement in GPA, MPA, and EGPA (defined as per CHCC 2012) observed at baseline and on follow-up

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Overall, 53 of the 66 (80.3%) patients were positive for PR3-ANCA and 13 of the 66 (19.7%) patients were positive for MPO-ANCA by the LIA. The diagnosis, clinical features, and ANCA by IIF were compared between the PR3 and MPO groups. As shown in [Table 2], the median age of the PR3 group was 50 years, whereas it was 56 years in the MPO group. The disease duration was similar in both the groups. In the PR3 group, the IIF staining pattern in 49 of 53 patients (92.45%) showed c-ANCA, in 3 patients (5.66%) the IIF staining was negative, and in one patient (1.9%) the pattern was atypical. In the MPO group, 13 of 13 (100%) showed the p-ANCA staining pattern by IIF.
Table 2: Comparison of diagnosis, ANCA staining pattern, age, duration of disease by PR3 and MPO status

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[Table 3] shows the comparison of organ involvement between PR3 and MPO groups. The frequency of renal involvement as manifested by acute kidney injury (AKI) or chronic kidney disease (CKD) is similar in both the groups. AKI was seen in 44.73% vs. 27.27% in PR3 and MPO, respectively; whereas CKD was present in 7.9% vs. 9.09% in PR3 and MPO, respectively.
Table 3: Comparison of organ involvement (clinical features) in patients with ANCA associated vasculitis (n = 66) by PR3 and MPO status

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Pulmonary involvement was observed in 84.9% of the PR3 patients vs. 69.2% in the MPO group (P = 0.18). Other organs, namely, eye, nervous system, gastrointestinal, and myocarditis, occurred in similar frequency in both the groups. ENT involvement was significantly more frequent in the PR3 group when compared with the MPO group (P = 0.009).

The median follow-up period was 18 vs. 12 months in the PR3 and MPO groups, respectively. Eight patients (12.12%) died during the study period. The Birmingham Vasculitis Activity Score (BVAS) at baseline and 6 months showed a decreasing trend. Some patients whose data were available after the 6-month follow-up period also showed a considerable decrease in the BVAS [Figure 1]. An equal proportion of patients had received cyclophosphamide as the first induction treatment in both the PR3 and MPO groups. However, many patients relapsed after the first induction in the PR3 group, compared with the MPO group [Table 4]. Consequently, a significantly higher proportion of patients in the PR3 group required rituximab for second induction treatment [Table 4]. However, there was no significant difference in mortality and permanent organ damage in both the PR3 and MPO groups [Table 4].
Figure 1: Diagram showing disease activity (BVAS) from the time patients were enrolled in the study till a minimum of 6 months’ follow-up (data of some patients whose follow-up was possible for more than 6 months are also depicted here)

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Table 4: Shows the important outcome variables

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  Discussion Top

We tested for the presence of ANCAs by IIF as well as for PR3-ANCA and MPO-ANCA in 66 patients with AAV. By IIF, c-ANCA positivity was higher when compared with p-ANCA positivity (74.24% vs. 19.7%): one patient had atypical ANCA positivity and three patients were ANCA-negative. However, all had either PR3-positive or MPO-positive test. The PR3 antibody was positive in 80.30%, whereas MPO was positive in 19.7% of the patients.

A study done by a Dutch–Danish group found that c-ANCA was associated with GPA and corresponded to PR3 titers, especially in active diseases.[2],[7],[39] A majority of patients with MPA were also found to produce ANCAs staining the perinuclear area of neutrophils and monocytes (p-ANCA), which were associated with MPO.[2] This study also stated that ANCA positivity would be considered only if both the IIF test and the direct ELISA for PR3-ANCA or MPO-ANCA were clearly positive.[2],[18],[19],[20] The importance of this combined ANCA testing approach was widely confirmed subsequently.[16],[17],[18],[19],[20],[21] A retrospective study was done by Weidner et al.[26] who compared patients based on serology. In this study, mortality and rate of relapse of end-stage renal disease were more in PR3 + patients, whereas in our study mortality was significantly higher in MPO + patients. The rate of relapse was much more in PR3 + patients in our study. As in our study, this study also undermines the prognostic importance of ANCA serology as PR3-ANCA had more relapses and more lung and upper respiratory tract involvement.

Lung involvement in GPA was found to be higher when compared with MPA and EGPA in our study. Also, patients with PR3 positivity had more frequent pulmonary involvement when compared with MPO-positive patients, though not statistically significant. This is also confirmed by many studies.[20],[21],[22],[23]

In our study, 50.9% of the GPA had kidney involvement, whereas 85.71% of the MPA had kidney disease. An Indian study by Kumar et al.[9] showed that 33% of the patients had kidney involvement. A German study done by the nephrology unit studied outcome analysis based on PR3 and MPO serology. As all patients included in this study had kidney involvement, it focussed more on the different types of renal manifestations.[8],[10],[26],[40]

Kidney involvement in AAV is characterized by pauci-immune necrotizing and crescentic glomerulonephritis with rapidly progressive glomerulonephritis.[24],[25],[26],[27],[28] Even though there are no qualitative differences in glomerular lesions in patients with GPA or with MPA, chronic damage is significantly higher in MPA (and/or p-ANCA-positive patients) than in GPA (and/or C-ANCA-positive patients).[11] In our study, renal involvement either AKI or rapidly progressive renal failure (RPRF) was more frequent in the PR3 group when compared with the MPO group, though not statistically significant.

In our study, the GPA group had a higher percentage of ENT involvement when compared with MPA and EGPA, but the difference was not statistically significant. But going by the PR3 and MPO status only, the PR3-positive group had significantly higher percentage of ENT involvement. This result was consistent with other studies, which showed that GPA and PR3 have higher percentage of sinonasal involvement.[9],[12],[13],[25],[41]

Ophthalmic involvement was seen in 36.36% of the total cohort. Of the 24 patients who had eye involvement, 17 patients had this as the initial manifestation of the disease. Studies have demonstrated that eye could be the initial and most important manifestation in AAV patients.[14],[18],[31],[35] Even though GPA had more patients with ophthalmic manifestations than MPA (37.73% vs. 14.28%), the association was not significant (P = 0.334). Around 40% of EGPA had ophthalmic involvement.[14],[18],[29],[30],[31],[35]

There was no significant difference in the prevalence of neurological manifestations between the three groups (P = 0.89, 0.105, and 0.2 for GPA vs. MPA, GPA vs. EGPA, and MPA vs. EGPA, respectively). There was also no significant difference in neurological manifestations between the PR3 and MPO groups. Neurological manifestations were seen in the form of pachymeningitis and neuropathies, and one patient in the GPA group even had cerebrovascular accident which was not attributable to any other causes. Many studies have shown that nervous system manifestations are serious manifestations and need urgent immunosuppression.[8],[10],[26],[40]

Gangrene, which is usually associated with MPA more than GPA, almost does not occur in EGPA.[9],[15],[33] However, in our cohort, all six patients who had gangrene as a manifestation of AAV were clinically GPA with PR3 serology positive. Myocarditis, a rare life-threatening manifestation, in the setting of AAV can be seen in all the three groups.[13],[15],[32],[41] In our cohort, out of the 10 patients who had myocarditis, 9 were GPA, all being PR3-positive. The other patient was MPA. There was no statistical significance between the PR3 and MPO groups.

Permanent organ damage either due to disease or treatment related was equally seen in the PR3 and MPO groups [Table 4]. Studies have shown that AAV as a disease is notorious to cause organ morbidity.[7],[9],[13],[16],[34],[39]

An equal proportion of patients in the PR3 and MPO groups received cyclophosphamide for induction.[4] Consistent with other studies,.[39],[40],[41],[42],[43] our GPA and PR3 group had more relapses, and thus 21 of 53 (39.6%) PR3 patients needed rituximab as a second induction therapy. In our study, relapsed or refractory patients showed good response to rituximab, which was consistent with the landmark RAVE study.[43] Two patients in the EGPA group were given cyclophosphamide for peripheral neuropathy. The other two achieved remission with oral steroids and azathioprine within 6 months.

Our study had few strengths. It has given the insight into the clinical features as well as it has made the classification easier based on the serology, viz., PR3 vs. MPO. There is no such study according to our knowledge in India which has looked after the correlation between the serology and clinical profile and their long-term outcomes.[36],[37],[38]

Also, it had few limitations. Data included old as well as new patients; hence, disease activity, frequency of relapses, and treatment response were obtained from the past records as well. A larger cohort is still needed to have the more accurate data, and long-term follow-up is required for the said cohort to see the frequency of relapses and rate of continuous remission.

After analyzing the aforementioned results, we propose to classify AAV based on the serology into anti-PR3 antibody-positive and anti-MPO antibody-positive-associated disease. It makes classification of AAV easier as there is no much difference between the two classification systems, i.e., serological and clinical.

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Conflicts of interest

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]


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