Classification Of Vasculitis Research Articles

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

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

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

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. 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 35years, 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.

Systemic vasculitis involving the kidney: the nephropathologist's point of view.

Kidneys are often targets of systemic vasculitis (SVs), being affected in many different forms and representing a possible sentinel of an underlying multi-organ condition. Renal biopsy still remains the gold standard for the identification, characterization and classification of these diseases, solving complex differential diagnosis thanks to the combined application of light microscopy (LM), immunofluorescence (IF) and electron microscopy (EM). Due to the progressively increasing complexity of renal vasculitis classification systems (e.g. pauci-immune vs immune complex related forms), a clinico-pathological approach is mandatory and adequate technical and interpretative expertise in nephropathology is required to ensure the best standard of care for our patients. In this complex background, the present review aims at summarising the current knowledge and challenges in the world of renal vasculitis, unveiling the potential role of the introduction of digital pathology in this setting, from the creation of hub-spoke networks to the future application of artificial intelligence (AI) tools to aid in the diagnostic and scoring/classification process.

A scoping review of vasculitis as an immune-related adverse event from checkpoint inhibitor therapy of cancer: Unraveling the complexities at the intersection of immunology and vascular pathology

Background/purposeVasculitis as an immune-related adverse event (irAE) from checkpoint inhibitor therapy (ICI) to treat cancer is a rare clinical event, and little is known regarding its nosology, clinical manifestations, or response to treatment and outcomes. MethodsTo address these gaps, we used the Preferred Reporting Items for Systemic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) framework to further define this complication. Two independent PUBMED searches in September and November of 2022 revealed 127 publications with 37 excluded from title by relevance, 43 excluded by article type, and 23 excluded due to lack of biopsy results, or biopsy negative for vasculitis. Twenty-nine documented cases from 24 publications were included for final analysis. Basic demographics, ICI details, timing of onset of vasculitis symptoms, irAE treatment and outcomes were collected. The vasculitides were classified using 2022 ACR/EULAR Vasculitis Classification Criteria as well as 2012 Revised Chapel-Hill Nomenclature. Adaptations from Naidoo et al. 2023 [1] consensus definitions for irAEs were used and efforts were made to classify steroid-responsive versus unresponsive irAEs. ResultsOf the 29 cases reviewed, the average age of patients was 62.1 ± 11.0, composed of 58.6 % (n = 17) male and 41.3 % (n = 12) female. Prominent cancer types were lung cancer (41.4 %; n = 12), melanoma (41.4 %; n = 12), and renal cancer (10.3 %; n = 3), with majority being stage 4 (75.9 %, n = 22) and stage 3 (10.3 %, n = 3). Only 8 cases met the ACR/EULAR criteria, and by Chapel-Hill Nomenclature, approximately a third were small-vessel vasculitis (31.0 %; n = 9) with n = 4 positive for ANCA. Most biopsies were taken from the skin (37.9 %, n = 11) and kidney (24.1 %, n = 7). Patients were either treated with single (65.5 %, n = 19), dual (17.2 %; n = 5), or sequential (17.2 %; n = 5) ICI regimen which included anti-PD-1 therapy in all but one case, with mean of 8.7 ± 10.5 cycles received. Mean time to onset of symptoms from start of ICI was 7.2 ± 7.8 months, with 55.2 % occurring >3 months since the initial immunotherapy. Vasculitis treatment included glucocorticoids in 96 % of cases and immunotherapy was often discontinued (44.8 %; n = 13). Clinical improvement of irAE was documented in 86.2 % (n = 25). Data were missing in terms of fate of ICI (34.5 %; n = 10) and tumor outcomes (41.4 %; n = 12). Cancer progressed in 20.7 % (n = 6), stable in 34.5 % (n = 10) cases, and 6 patients died of all-causes. ConclusionVasculitis as an irAE appears clinically heterogeneous and rare. Among reported cases with adequate documentation, vasculitis is of delayed onset following the initiation of immunotherapy. Outcomes of ICI-vasculitis were generally favorable, responding to glucocorticoids and immunotherapy withdrawal. There is an urgent need for more standardized reporting of rare irAEs such as vasculitis to clarify clinical risks, classification, relationship to immunotherapy and outcomes.

Nationwide epidemiological survey of polyarteritis nodosa in Japan in 2020.

Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis that predominantly affects medium-sized arteries. With advances in our understanding of the pathogenesis and classification of vasculitis, PAN and microscopic polyangiitis (MPA), a disease of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV), were separated from the group of diseases previously diagnosed as periarteritis nodosa (PN) at the Chapel Hill Consensus Conference (CHCC) in 1994 (1).

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

To evaluate the ACR/EULAR 2022 criteria for ANCA-associated vasculitides (AAV) classification and compare them with the European Medicines Agency (EMA) algorithm and with classification based only on ANCA serology. In the analysis, 374 cases (47% female) were classified according to the EMA algorithm, ANCA serology and ACR/EULAR criteria. The agreement rate was calculated using the kappa (κ) statistic. Under EMA, 192 patients were classified as granulomatosis with polyangiitis (GPA), 159 as microscopic polyangiitis (MPA) and 23 as eosinophilic granulomatosis with polyangiitis (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 13 (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 (83.9%) 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. 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.

Системный васкулит: исторические аспекты

Systemic vasculitis is a severe multi-organ disease in which early diagnosis and treatment significantly improve the prognosis. The accumulated understanding of the pathogenesis of systemic vasculitis and the emergence of new treatment options for these diseases have become an incentive to revise existing definitions, nomenclature and develop a new classification. Improving the classification can help reduce the likelihood of diagnostic errors. The presented article is devoted to the historical aspects of the formation of modern nomenclature and classification of systemic vasculitis.

Clinicopathological characteristics and key therapeutic options for liver involvement with vasculitis

Vasculitis, involving any levels of vessels throughout the body, has variable nonspecific clinical presentation and complicated classification, hence, the diagnose is difficult. The liver is not the major organ involved, so it is prone to overlook vasculitis-associated liver injuries. The main manifestations of vasculitis involving the liver include abnormal liver biochemistry test (mainly increase of cholestatic liver enzymes), portal hypertension, and hepatic occupying lesions. Treatment principles are primarily directed at systemic immunosuppressive therapy for vasculitis. This review summarized the classification of vasculitis, major presentations of liver involvement in vasculitis, and the principles of treatment, to improve the awareness of the rare vascular diseases.

Antineutrophil cytoplasmic antibody-associated vasculitis classification by cluster analysis based on clinical phenotypes: a single-center retrospective cohort study.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) refers to a group of small vessel inflammatory disorders. Overlapping clinical phenotypes of AAV subgroups continually provoke controversies over their diagnostic and classification criteria. Using the agglomerative hierarchical clustering method, we classified 210 Korean patients diagnosed with AAV into mutually exclusive clusters according to Birmingham Vasculitis Activity Score items, ANCA specificity, sex, and age. We analyzed the resulting clusters' outcomes to investigate the clinical significance of the classification. We proposed a distance-based algorithm of patient assignment and explored its clinically relevant modification. In total, 116 patients (55%) had microscopic polyangiitis, 53 (25%) had granulomatosis with polyangiitis, and 42 (20%) had eosinophilic granulomatosis with polyangiitis. Our model grouped the patients into five clusters, namely, "limited proteinase 3 (PR3)-ANCA vasculitis," "generalized PR3-ANCA vasculitis," "ANCA-negative vasculitis," "renal-limited vasculitis," and "myeloperoxidase-ANCA vasculitis." Patients clustered under "generalized PR3-ANCA vasculitis" had a higher relapse rate (hazard ratio [HR] = 2.12, P = 0.067). The incidence of end-stage renal disease was higher in patients belonging to the "renal-limited vasculitis" cluster (HR=1.50, P=0.03), and those in the "ANCA-negative vasculitis" cluster experienced a relatively milder clinical course of AAV (mortality = 0). Because the clusters were naturally derived from their distinguished phenotypes and have different clinical courses, our clustering method may be a more clinically relevant classification system for AAV, revealing its phenotypic diversity. We also proposed a simple and intuitive distance-based assignment algorithm, which can be easily modified according to specific clinical needs. Key Points • In this study with a single-center AAV cohort, we showed that AAV can be divided into five distinct subclasses with different disease courses based on the clinical and laboratory features of the patients. • Our study revealed ethnic differences in AAV manifestation and suggests that physicians may need to analyze their own AAV patients to assess the disease status of AAV patients. • We proposed a distance-based cluster membership assignment method that can be clinically modified to fit the specific purpose of grouping patients.

Wounds caused by vasculitis-Current classification, diagnostics and treatment

Wounds of the skin can have very different causes. Especially in clinically atypical or non-healing wounds, the very heterogeneous group of vasculitides is of particularly important differential diagnostic significance. Nowadays, the classification of vasculitis is based on the affected vessels according to the Chapel Hill consensus conference. Thus, potentially any part of the vascular system can be affected. It becomes clear that there is often arisk of systemic diseases with high interdisciplinary relevance.Clinically, the usually very painful wounds in cutaneous vasculitis develop from necrosis and are typically surrounded by an erythematous-livid rim in the florid phase. In addition to clinical inspection, the histopathological examination of biopsies is of particular importance in the usually extensive diagnostic work-up.Therapeutically, adequate wound treatment should always be performed with afocus on pain prevention and infection prophylaxis. In the case of edema, compression therapy also supports wound healing. In addition, it is often necessary to initiate systemic treatment with immunosuppressive or immunomodulating drugs. Whenever possible, causally relevant factors and comorbidities should be diagnosed early and avoided or treated. Otherwise, there is arisk of severe or even fatal disease progression.

Cutaneous Small Vessel Vasculitis: A Practical Guide to Diagnosis and Management.

Cutaneous vasculitis may be a cutaneous manifestation of systemic vasculitis, a skin-limited variant of systemic vasculitis, or a type of single-organ vasculitis limited to the skin. Careful evaluation is necessary to distinguish these possibilities, differentiate skin-limited from systemic disease, and identify important underlying conditions, if present. Appropriate management depends on disease type and severity. In the case of cutaneous small vessel vasculitis (CSVV), treatment is primarily based on case reports and expert opinion, using a range of immunomodulatory or immunosuppressive therapies. This manuscript presents a systematic and stepwise approach to the evaluation of patients presenting with cutaneous vasculitis, as well as the management of those diagnosed with CSVV, using best available evidence. Studies relevant to the classification, evaluation, and management of skin vasculitis are ongoing.

Differentiation of lower limb vasculitis from physiological uptake on FDG PET/CT imaging.

To analyze the difference of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) uptake between vasculitis and non-vasculitic patients in PET/CT imaging and the factors related to vascular uptake in non-vasculitic patients. To investigate the feasibility of identifying vasculitis of the lower limb and physiological uptake with delayed imaging. Among 244 patients who underwent PET/CT examination, imaging features of patients with or without vasculitis were retrospectively analyzed. The factors related to FDG uptake in the lower limb vessels of non-vasculitic patients were analyzed. Another 44 patients with suspected systemic vasculitis in PET/CT were prospectively studied to analyze the efficacy of delayed imaging on differentiating vascular uptake in lower limbs. In PET/CT imaging of patients with vasculitis, involvement of trunk vessels showed segmental or diffuse FDG distribution. Lower limb vascular involvement showed reticular uptake accompanied by nodular or patchy changes. In non-vasculitic patients, vascular uptake mainly showed linear uptake in lower limb vessels and there was no significant difference in uptake degree compared with vasculitis patients. Body weight and interval time were the independent influence factors of vascular uptake in lower limbs of non-vasculitic patients. In delayed imaging, lower limb vasculitis all showed reticular uptake and physiological uptake all showed a linear pattern. ROC analysis showed the change rate of SUVmax (≥ 20%) between early and delayed imaging could delineate physiological vascular uptake with a sensitivity of 100% and specificity of 81.0%. When PET/CT is used for the diagnosis and classification of vasculitis, the physiological uptake of lower limb vessels may mislead the diagnosis. PET/CT imaging features or delayed imaging improved diagnostic efficacy.

Inflammation and thrombo-occlusive vessel signalling in benign atrophic papulosis (Köhlmeier-Degos disease).

Although the merely cutaneous, benign form of the extremely rare disease atrophic papulosis (Köhlmeier-Degos disease) may occasionally develop into the systemic, malignant form with time, it is unclear whether it exhibits any systemic characteristics. To determine whether benign atrophic papulosis exhibits inflammatory and thrombo-occlusive signals and to classify it according to the Chapel-Hill classification of vasculitis. In a monocentric, controlled study, levels of cytokines (IL-1β, IL-6, IL-8, IFNγ, MCP-1, VEGF, TNFα, TGF-β1), antiphospholipid antibodies (cardiolipin IgG/A/M, cardiolipin IgG, cardiolipin IgM, β2-glycoprotein IgG/A/M, phosphatidyl choline, phosphatidyl serine, phosphatidyl inositol, phosphatidyl ethanolamine and sphingomyelin A), antibodies against proteinase-3 IgG and myeloperoxidase IgG, antinuclear antibodies and extractable nuclear antigen were assessed in blood samples of six benign atrophic papulosis patients and six age- and sex-matched healthy controls. IL-8 was only detectable in patients' serum. VEGF was reduced and cardiolipin IgG/A/M and β2-glycoprotein antibodies were increased in the patients' group. ANA were only detected in three patients, and ENA were negative throughout. No differences were detected between the other investigated markers. This is the first study evaluating systemic inflammatory and thrombo-occlusive vessel signalling in benign atrophic papulosis and provides evidence of a non-antineutrophil cytoplasmatic antibodies immune-complex small vessel vasculitis according to the Chapel-Hill classification. These findings corroborate its systemic character despite the apparent missing involvement of systemic organs.

Classification of systemic vasculitis: evolution from eponyms to modern criteria

Systemic vasculitis is a manifold group of systemic autoimmune diseases characterized by the inflammation of the blood vessels. The first clinical cases of systemic vasculitis were described in the Middle Ages, and most of the currently recognised nosological forms were reported in the first half of the 20th century. The first attempt to create a united classification of vasculitis was performed by P. Zeek in 1952. In the following decades accumulation of the data on the etiology and pathogenesis of different vasculitis guided researchers from different countries in their attempts to improve classification. The main principles of classification were the size of the affected blood vessels, disease etiology and pathogenesis. In 1990 American College of Rheumatology (ACR) published classification criteria for seven forms of the systemic vasculitis, that gave a significant contribution to the conduction of large-scale studies in this field. However, the first international nomenclature of vasculitis was developed only in 1994 during the Consensus Conference in Chapel Hill. Revised and augmented version of this nomenclature was created in 2012 and is still valid. An important step in the development of the classification of vasculitis was a joint project of ACR and EULAR aimed to develop new diagnostic and classification criteria for vasculitis (DCVAS). The first result of this project are the new classification criteria for granulomatosis with polyangiitis, microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis published in 2022. In general, the evolution of the classification of vasculitis occurs under the influence of the progress in the understanding of their etiology and pathogenesis.

Plasmapheresis for systemic vasculitis.

Systemic vasculitides include a variety of, and numerous diseases. In 2012, the International CHAPEL HILL Consensus Conference (CHCC2012) led to a major reorganization of the classification of vasculitis, and this is still in wide use today. Although the results of plasmapheresis for individual diseases have been sometimes shown, there are few systematic reviews that discuss the effects along with vasculitis classification. Therefore, we will discuss the efficacy and the latest evidence for each vasculitis according to the CHCC 2012 classification in this review. This review provides a comprehensive overview of the estimation of plasmapheresis in each of the vasculitides, with a particular focus on small vasculitides, which have recently discussed frequently. For some time now, plasma exchange therapy (PEX) has been frequently used and is expected to be effective in some diseases, most of which are included in small vessel vasculitides. In particular, data showing efficacy have been accumulated for immune complex vasculitis, and the recommendation seems to be high. For instance, anti‐GBM nephritis, concomitant use of PEX is essential and strongly recommended. On the other hand, for ANCA‐related vasculitis among small vessel vasculitis, RCTs have recently shown negative results. In particular, the PEXIVAS trial statistically showed that PEX has no potential to reduce the mortality and renal death in AAV, but the ASFA, ACR, and KDIGO guidelines following this trial all regard PEX as salvage therapy or selective treatment for severe cases. As plasmapheresis is often performed in combination with other therapies, it is difficult to evaluate to clarify its efficacy on its own, and this predisposition may be pronounced in vasculitis, a rare disease. Although statistically significant differences are not apparent, the diseases that show a trend toward efficacy may possibly include treatment‐sensitive subgroups. Further analysis is expected in the future.

POS-128 CASE SERIES OF PERI-RENAL COLLECTION IN PATIENTS WITH RAPID PROGRESSIVE RENAL FAILURE-LIKE PRESENTATION– A DIAGNOSTIC CHALLENGE

Background: The vasculitides are defined by the presence of inflammatory leukocytes in vessel walls with reactive damage to mural structures. The typical framework for classification of vasculitides is based upon the predominant size (large, medium, or small) of the involved vessels as per CHCC 2012 which also includes variable vessel vasculitis and single organ vasculitis. In the current case series – both MPA, PAN behaving similarly – questioning the integrity of CHCC and an unmet need for new etiological classification for vasculitis.

Imaging features of 18F-FDG PET/CT in different types of systemic vasculitis.

To analyze 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) image features in different types of systemic vasculitis and explore its classification and diagnostic significance for systemic vasculitis. Clinical and 18F-FDG PET/CT imaging data of 71 consecutive patients (34 males, 37 females, mean age 53.4 ± 20.5years) who were examined at Peking University People's Hospital and diagnosed with active systemic vasculitis were analyzed retrospectively, and 18F-FDG PET/CT imaging features of different types of systemic vasculitis were analyzed in patients with positive 18F-FDG PET/CT findings. The proportions of large-, medium-, small-, and variable-vessel vasculitis were 36.6%, 15.5%, 29.6%, and 18.3%, respectively, and 93.0% of patients had positive findings on PET/CT, of which 63.6% had vascular involvement and 53.0% had extravascular involvement. Different types of vasculitis had different lesion sites, distribution patterns, and morphological changes. Large-vessel vasculitis mainly affected the aorta and its branches to the head and neck. Takayasu arteritis showed segmental involvement of the vascular and morphological changes of the vessel wall. Giant cell arteritis manifested as diffuse vascular involvement, which usually involved the temporal artery and the abdominal aorta and its branches. Medium-vessel vasculitis polyarteritis nodosa manifested as diffuse vascular involvement of both lower extremities. Small-vessel vasculitis anti-neutrophil cytoplasmic antibody-associated vasculitis manifested as granulomatous inflammation of extravascular regions. Variable-vessel vasculitis Behcet's disease involved both blood vessels and extravascular regions. Different types of systemic vasculitis show characteristic manifestations in 18F-FDG PET/CT images, which may be useful for the diagnosis and classification of systemic vasculitis. • Determining an early diagnosis of systemic vasculitis may be challenging. • Different types of systemic vasculitis show characteristic manifestations in 18F-FDG PET/CT images. • 18F-FDG PET/CT may be useful for the diagnosis and classification of systemic vasculitis.

Revisiting the question of cutaneous vasculitis classification

Currently, there is no generally accepted terminology and classification of vasculitis and vascular cutaneous disorders. In Russia there are various approaches to the classification of cutaneous vasculitis vascular lesions are classified according to clinical signs, etiology and pathogenesis. Significant difficulties are caused by the lack of a unified terminology, clear diagnostic criteria for vasculitis and the existence of a large number of duplicate names, among which there are many eponymous terms. This issue is one of the most complex, confusing and debatable not only in dermatovenereology, but also in other disciplines. Modern principles of diagnosis of cutaneous vasculitis are based on an integrated assessment of the data of the disease history, clinical picture, laboratory and instrumental methods of examination. For standardization of definitions and diagnostic criteria, it is necessary, first of all, to adopt a unified interdisciplinary classification of vasculitis, which will be based on the etiopathogenetic principle. The applied unified classification of cutaneous vasculitis is proposed for discussion.

Updates in cutaneous manifestations of systemic vasculitis.

The main purpose of this review is to present newly reported cutaneous manifestations of systemic vasculitis, updates in investigations to verify systemic involvement in cases with cutaneous vasculitis and new therapeutic guidelines. The spectrum of COVID-19-related vasculitis is also covered. Only a few reports highlighted new cutaneous presentations or associations with some systemic vasculitic entities. For example, the association of inflammatory disorders with Takayasu arteritis, the importance of considering Kawasaki disease in febrile children with erythema nodosum, the development of necrotic ulcers on fingers and toes in Behçet's disease and the possible presence of polyarteritis nodosa-like pathological features in vulvar ulcers of Behçet's disease. New attempts to classify cutaneous manifestations of giant cell arteritis (GCA) and antineutrophil cytoplasmic antibody-associated vasculitis (AAV) and the diagnostic investigations for cutaneous vasculitis cases to verify systemic involvement are discussed. Treatment of systemic vasculitis with cutaneous vasculitis should be tailored according to disease status. A plethora of reports in the past 2 years focused on the broad spectrum of COVID-19 vasculitic manifestations. Although newly reported cutaneous manifestations of systemic vasculitis are relatively uncommon, the plethora of reports in the past 2 years on COVID-19 vasculitis necessitates the expansion of the classification of vasculitis associated with probable cause to include severe acute respiratory syndrome coronavirus-2 (SARS-Cov-2) vasculitis.

Classification of ANCA-associated vasculitis: differences based on ANCA specificity and clinicopathologic phenotype.

The classification of vasculitis according to a schema with universal acceptance is challenging, given the heterogeneous and protean nature of these diseases. Formal nomenclature and classification criteria for anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) have suffered several changes since their first description; none provides comprehensive diagnostic and classification criteria. Different factors account for the difficulties in the classification of vasculitis, including the incomplete understanding of the pathogenesis, the multisystemic nature of the disease, the non-specific patterns of vascular involvement, the overlap between entities, and the presence of various classification systems. The present article reviews the classification of AAV considering different points of view, including clinical, serologic, pathogenetic, organ predilection, therapeutic, and prognostic factors, and provides perspectives on future challenges in the understanding of AAV. There is an unmet need for a unifying view of the disease spectrum that considers the constantly evolving paradigms.