Classification Criteria for ANCA Associated Vasculitis - Ready for Prime Time?

PURPOSE OF REVIEW: This review aims to summarize the evolution and recent developments in the classification of ANCA associated vasculitis (AAV) and to summarize evaluations of the 2022 ACR/EULAR classification criteria of AAV in several cohorts. RECENT FINDINGS: The classification of AAV has been a field of controversy for some time. The parallel existence of classification criteria and disease definitions produced some overlap in classification, leading to challenges when comparing different cohorts. The 2022 ACR/EULAR classification criteria derived from the largest study ever conducted in vasculitis account for significant changes in vasculitis classification with the integration of ANCA and modern imaging. These criteria show good performance compared to previous ones but also raise questions as ANCA serotypes have substantial impact on classification. In addition, there are some discrepancies with earlier agreed histopathological features of AAV disease phenotypes. During the last 35 years, several sets of classification criteria have evolved to facilitate epidemiologic studies and clinical trials in AAV. While some of these criteria have been in use for many years, they were criticized due to either not using ANCA or not integrating surrogate markers for vasculitis but also due to overlapping when used in parallel. The long-awaited new ACR/EULAR criteria for AAV were published in 2022 and are the result of a large international study, introducing for the first time ANCA and modern imaging in the classification of AAV. Though the criteria show good performance, they bring several other challenges with practical application.

Evaluation of the ACR/EULAR 2022 criteria for classification of ANCA-associated vasculitis in a population-based cohort from Sweden.

OBJECTIVE: To evaluate the ACR/EULAR 2022 criteria for AAV classification and compare it to the EMA algorithm and to classification based only on ANCA serology. METHODS: In the analysis, 374 cases (47% female) were classified according to EMA algorithm, ANCA serology, and ACR/EULAR criteria. The agreement rate was calculated using the kappa (κ) statistic. RESULTS: Under EMA, 192 patients were classified as GPA, 159 as MPA, and 23 as EGPA. The ACR/EULAR criteria classified 199 patients as GPA, 136 as MPA, and 22 as EGPA. Four patients (1.1%) met criteria of two disease categories, and thirteen (3.5%) were unclassifiable. The observed agreement between EMA and ACR/EULAR was 85% for GPA, 75% for MPA, and 96% for EGPA. The unweighted κ statistic was 0.66 (95% CI 0.60-0.74). Of the 188 PR3-ANCA-positive patients, 186 (98.9%) were classified as GPA using ACR/EULAR criteria, and 135 of 161 (83.8%) MPO-ANCA-positive patients were classified as MPA. With a classification solely based on ANCA-specificity, agreement with ACR/EULAR was 99% for GPA and 88% for MPA. CONCLUSIONS: EMA and ACR/EULAR classification give similar results. A small proportion of patients cannot be classified or fall into two categories. Some patients exhibiting granuloma, a key feature of GPA, are nevertheless classified as MPA, conflicting with the current view of histopathology of AAV. There is high agreement of ANCA-based classification with that of ACR/EULAR, reflected in the considerable weight granted to ANCA in the new criteria. These crucial elements within the new criteria necessitate a consensus discussion among field experts.

Stable incidence but increase in prevalence of ANCA-associated vasculitis in southern Sweden: a 23-year study.

OBJECTIVE: To update the epidemiology of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) in a defined geographical area of southern Sweden. METHODS: The study area comprised 14 municipalities with a combined adult population (≥18 years) of 623 872 in 2019. All cases diagnosed with AAV in 1997-2019 in the study area were included in the estimate of incidence. Diagnosis of AAV was verified by case record review, and cases were classified using the European Medicines Agency algorithm. Point prevalence was estimated on 01 January 2020. RESULTS: Three hundred and seventy-four patients (median age 67.5 years, 47% female) were diagnosed with new-onset AAV during the study period. One hundred and ninety-two were classified as granulomatosis with polyangiitis (GPA), 159 as microscopic polyangiitis (MPA) and 23 as EGPA. The average annual incidence/million adults was 30.1 (95% CI 27.0 to 33.1) for AAV: 15.4 (95% CI 13.3 to 17.6) for GPA, 12.8 (95% CI 10.8 to 14.8) for MPA and 1.8 (95% CI 1.1 to 2.6) for eosinophilic GPA (EGPA). Incidence was stable during the study period, 30.3/million 1997-2003, 30.4/million 2004-2011 and 29.5/million 2012-2019. The incidence increased with age and was highest in age group 70-84 years (96/million adults). On 1 January 2020, the prevalence was 428/million adults and was higher in males than in females (480 vs 378/million). CONCLUSIONS: The incidence of AAV in southern Sweden was found stable over the course of 23 years; while the prevalence has increased, which might indicate better management and treatment of AAV resulting in improved survival.

Infection is associated with increased risk of MPO- but not PR3-ANCA-associated vasculitis.

OBJECTIVES: To determine whether development of ANCA-associated vasculitis (AAV) shows a relationship with a prior infection and if prior infection affects disease characteristics and outcome. METHODS: All incident cases of AAV diagnosed in a defined region of Sweden from 2000 through 2016 were identified. For each case, 10 individuals from the general population, matched for age, sex and area of residence, were selected. Infections occurring in AAV patients and controls prior to the date of AAV diagnosis (index date for respective controls) were identified using an administrative database. Conditional logistic regression models were used to calculate odds ratios (OR) of developing AAV. Occurrence, clinical characteristics and outcome of AAV were analysed with respect to prior infection. RESULTS: Two-hundred and seventy patients with AAV (48% female) and 2687 controls were included. Prior to diagnosis/index date, 146 (54%) AAV patients had been diagnosed with infection vs 1282 (48%) controls, with OR for AAV 1.57 (95% CI 1.18, 2.19) in those with infections of the upper respiratory tract and 1.68 (1.02, 2.77) in those with pneumonia. Difference from controls was significant in patients with MPO-ANCA 1.99 (95% CI 1.25, 3.1) but not in those with PR3-ANCA 1.0 (0.61, 1.52). Patients with prior infection showed higher disease activity at AAV diagnosis. No differences in disease characteristics, comorbidities or outcome in those with and without prior infections were observed. CONCLUSIONS: Respiratory tract infections are positively associated with development of MPO- but not PR3-ANCA vasculitis. Prior infection is associated with higher disease activity at AAV diagnosis.

Incidence and predictors of severe infections in ANCA-associated vasculitis: a population-based cohort study.

OBJECTIVE: To determine the incidence rate, predictors and outcome of severe infections in a population-based cohort of ANCA-associated vasculitis (AAV). METHODS: The study included 325 cases of AAV (152 female) diagnosed from 1997 through 2016 from a defined geographic area in Sweden. All severe infection events (requiring hospitalization and treatment with intravenous antimicrobials) were identified. The Birmingham vasculitis activity score (BVAS) was used to evaluate disease activity, and organ damage was assessed using the vasculitis damage index (VDI). Patients were followed from time of AAV diagnosis to death or December 2017. RESULTS: A total of 129 (40%) patients suffered at least one severe infection. In 2307 person-years (PY) of follow-up, 210 severe infections were diagnosed. The incidence rate of severe infections was 9.1/100 PY and was highest during the first year following AAV diagnosis at 22.1/100 PY (P < 0.001). Pneumonia, sepsis and urinary tract infection were the most common infections. Opportunistic infections constituted only 6% of all severe infections. In Cox regression analysis age and BVAS at diagnosis were the only factors independently predicting severe infection [hazard ratio: 1.54 (P < 0.001) and 1.27 (P = 0.001), respectively]. Severe infection was associated with poorer prognosis with respect to median VDI score 12 months post-AAV diagnosis, renal survival and mortality. Severe infections were the cause of death in 32 patients (22% of all deaths). CONCLUSION: . Severe infection is a common problem in AAV, with the most important prognostic factors being older age and high disease activity at diagnosis. Severe infections are associated with permanent organ damage and high mortality.