Eosinophilic granulomatous polyangiitis with central nervous system involvement in children: a case report and literature review.

Objective: To explore the clinical characteristics and treatment outcomes of children with central nervous system (CNS) involvement in eosinophilic granulomatosis with polyangiitis (EGPA). Methods: A child who presented with EGPA complicated by CNS involvement was admitted to our hospital in June 2023. The clinical features were analyzed retrospectively, and relevant literatures were reviewed to provide a comprehensive overview of this condition. Results: A ten-year-old girl, who had a history of recurrent cough and asthma accompanied by peripheral blood eosinophilia for eight months, was admitted to our hospital. On admission, spotted papules were visible on her hands and feet, bilateral pulmonary rales were audible. The laboratory examination revealed that the proportion of eosinophils (EOS) exceeded 10% of white blood cells, the anti-neutrophil cytoplasmic antibody (MPO-ANCA) was positive, the immunoglobulin G level was 15.80g/L, and the immunoglobulin E level was greater than 2500.00IU/mL. The imaging examination showed multiple patchy and nodular high-density shadows in both lungs as well as sinusitis. Pulmonary function tests indicated moderate ventilation and diffusion dysfunction. Bone marrow cytology demonstrated a significant increase in the proportion of eosinophils. Skin pathology confirmed leukocytoclastic vasculitis. During the hospitalization, the child had a convulsion. The magnetic resonance imaging (MRI) scan of the brain showed multiple abnormal signal shadows in the bilateral cerebral cortex and the electroencephalogram (EEG) showed epileptic waves. Following the administration of methylprednisolone pulse therapy in combination with cyclophosphamide treatment, her cough and asthma resolved, the skin rash disappeared without any further convulsions. We found that only a young EGPA patient with CNS involvement had been previously reported. The previously reported case began with long-term fever, weight loss, and purpuric rash. Both patients responded well to treatment with glucocorticoids and cyclophosphamide, experiencing significant improvement in their clinical symptoms and normalization of their peripheral blood eosinophils. Conclusion: The diagnosis of EGPA in children can be challenging. When a child is affected by EGPA, it is essential to remain vigilant for signs of CNS involvement. The treatment with glucocorticoids and cyclophosphamide is effective in managing EGPA in children.

Clinical Characteristics of EGPA Patients in Comparison to GPA Subgroup with Increased Blood Eosinophilia from POLVAS Registry.

Objective: To characterize the eosinophilic granulomatosis with polyangiitis (EGPA) population from the POLVAS registry depending on ANCA status and diagnosis onset, including their comparison with the granulomatosis with polyangiitis (GPA) subset with elevated blood eosinophilia (min. 400/µl) (GPA HE) to develop a differentiating strategy. Methods: A retrospective analysis of the POLVAS registry. Results: The EGPA group comprised 111 patients. The ANCA-positive subset (n = 45 [40.54%]) did not differ from the ANCA-negative one in clinics. Nevertheless, cardiovascular manifestations were more common in ANCA-negative patients than in those with anti-myeloperoxidase (MPO) antibodies (46.97% vs. 26.92%, p = 0.045). Patients diagnosed before 2012 (n = 70 [63.06%]) were younger (median 41 vs. 49 years, p < 0.01), had higher blood eosinophilia at diagnosis (median 4,946 vs. 3,200/µl, p < 0.01), and more often ear/nose/throat (ENT) and cardiovascular involvement. GPA HE comprised 42 (13.00%) out of 323 GPA cases with reported blood eosinophil count. Both GPA subsets had a lower prevalence of respiratory, cardiovascular, and neurologic manifestations but more often renal and ocular involvement than EGPA. EGPA also had cutaneous and gastrointestinal signs more often than GPA with normal blood eosinophilia (GPA NE) but not GPA HE. The model differentiating EGPA from GPA HE, using ANCA status and clinical manifestations, had an AUC of 0.92, sensitivity of 96%, and specificity of 95%. Conclusion: Cardiovascular symptoms were more prevalent in the ANCA-negative subset than in the MPO-ANCA-positive one. Since EGPA and GPE HE share similarities in clinics, diagnostic misleading may result in an inappropriate therapeutic approach. Further studies are needed to optimize their differentiation and tailored therapy, including biologics.

The Joint Vasculitis Registry in German-speaking countries (GeVas): subgroup analysis of 266 AAV patients.

OBJECTIVES: Prospective long-term observational data on the disease course of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) were missing in Germany to date. Therefore, the Joint Vasculitis Registry in German-speaking countries (GeVas) has been established to follow the course of patients with AAV. The aim of this study is to present baseline data of patients with newly diagnosed and relapsing AAV enrolled in the GeVas registry. METHODS: GeVas is a prospective, web-based, multicentre, clinician-driven registry for the documentation of organ manifestations, damage, long-term outcomes, and therapy regimens in various types of vasculitis. Recruitment started in June 2019. RESULTS: Between June 2019 and October 2022, 266 patients with AAV were included in the GeVas registry: 173 (65%) with new-onset and 93 (35%) with relapsing AAV. One hundred and sixty-two (61%) patients were classified as granulomatosis with polyangiitis (GPA), 66 (25%) as microscopic polyangiitis (MPA), 36 (13%) as eosinophilic granulomatosis with polyangiitis (EGPA), and 2 (1%) as renal limited AAV. The median age was 59 years (51-70 years, IQR), 130 (51%) patients were female. Most patients were ANCA positive (177; 67%) and affected by general symptoms, pulmonary, ear nose throat (ENT), renal and neurological involvement. For induction of remission, the majority of patients received glucocorticoids (247, 93%) in combination with either rituximab (118, 45%) or cyclophosphamide (112, 42%). CONCLUSIONS: Demographic characteristics are comparable to those in other European countries. Differences were found regarding ANCA status, frequencies of organ manifestations, and therapeutic regimens. The GeVas registry will allow longitudinal observations and prospective outcome measures in AAV.

Benralizumab versus Mepolizumab for Eosinophilic Granulomatosis with Polyangiitis.

BACKGROUND: Eosinophilic granulomatosis with polyangiitis (EGPA) is a vasculitis characterized by eosinophilic inflammation. Benralizumab, a monoclonal antibody against the interleukin-5α receptor expressed on eosinophils, may be an option for treating EGPA. METHODS: We conducted a multicenter, double-blind, phase 3, randomized, active-controlled noninferiority trial to evaluate the efficacy and safety of benralizumab as compared with mepolizumab. Adults with relapsing or refractory EGPA who were receiving standard care were randomly assigned in a 1:1 ratio to receive benralizumab (30 mg) or mepolizumab (300 mg) subcutaneously every 4 weeks for 52 weeks. The primary end point was remission at weeks 36 and 48 (prespecified noninferiority margin, -25 percentage points). Secondary end points included the accrued duration of remission, time to first relapse, oral glucocorticoid use, eosinophil count, and safety. RESULTS: A total of 140 patients underwent randomization (70 assigned to each group). The adjusted percentage of patients with remission at weeks 36 and 48 was 59% in the benralizumab group and 56% in the mepolizumab group (difference, 3 percentage points; 95% confidence interval [CI], -13 to 18; P = 0.73 for superiority), showing noninferiority but not superiority of benralizumab to mepolizumab. The accrued duration of remission and the time to first relapse were similar in the two groups. Complete withdrawal of oral glucocorticoids during weeks 48 through 52 was achieved in 41% of the patients who received benralizumab and 26% of those who received mepolizumab. The mean (±SD) blood eosinophil count at baseline was 306.0±225.0 per microliter in the benralizumab group and 384.9±563.6 per microliter in the mepolizumab group, decreasing to 32.4±40.8 and 71.8±54.4 per microliter, respectively, at week 52. Adverse events were reported in 90% of the patients in the benralizumab group and 96% of those in the mepolizumab group; serious adverse events were reported in 6% and 13%, respectively. CONCLUSIONS: Benralizumab was noninferior to mepolizumab for the induction of remission in patients with relapsing or refractory EGPA. (Funded by AstraZeneca; MANDARA ClinicalTrials.gov number, NCT04157348.).

COVID-19 and eosinophilic granulomatosis with polyangiitis or COVID-19 mimicking eosinophilic granulomatosis with polyangiitis?

Coronavirus disease 2019 (COVID-19) and eosinophilic granulomatosis with polyangiitis (EGPA) share similarities in clinical, imaging findings and may present with respiratory distress. Differentiating a new-onset EGPA from COVID-19 during the current pandemic is a diagnostic challenge, particularly if other EGPA symptoms are overlooked. Here in this study we reviewed the literature regarding EGPA patients with COVID-19 and patients who diagnosed with EGPA or suffered an EGPA flare mimicking COVID-19. We conducted a literature survey in PUBMED database using meshed keywords "COVID-19" and "EGPA", "COVID-19" and "eosinophilic granulomatosis with polyangiitis", "COVID-19" and "Churg Strauss Syndrome", to reveal previously reported cases involving EGPA patients who had COVID-19 infection, patients who suspected to have COVID-19 but eventually diagnosed with EGPA and patients with a known diagnosis of EGPA who suffered a flare but a COVID-19 infection was suspected initially. A total of 11 cases (6 literature cases, 5 cases from our clinic) were included in our study. Seven (63.6%) of the cases were defined as COVID-19 mimicker and 4 (36.4%) were EGPA with COVID-19. All of the cases in EGPA with COVID-19 group had a history of asthma. All of them had a positive PCR result and ground-glass opacities in thorax CT. In COVID-19 mimicker group, six (85.7%) patients had a history of asthma and other EGPA features that were observed were eosinophilia in 6 (85.7%). Our study provided clues regarding the EGPA/COVID-19 diagnostic challenge which may be useful in the current pandemic. Since none of the findings in COVID-19 are disease-specific, other conditions like EGPA should not be overlooked particularly in PCR negative patients and clinical, laboratory and imaging findings should be interpreted carefully. Furthermore, we did not observe poor outcomes in EGPA patients who had COVID-19.

A role for IL-33-activated ILC2s in eosinophilic vasculitis.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare but serious disease with poorly understood mechanisms. Here, we report that patients with EGPA have elevated levels of TSLP, IL-25, and soluble ST2, which are well-characterized cytokine "alarmins" that activate or modulate type 2 innate lymphoid cells (ILC2s). Patients with active EGPA have a concurrent reduction in circulating ILC2s, suggesting a role for ILC2s in the pathogenesis of this disease. To explore the mechanism of these findings in patients, we established a model of EGPA in which active vasculitis and pulmonary hemorrhage were induced by IL-33 administration in predisposed, hypereosinophilic mice. In this model, induction of pulmonary hemorrhage and vasculitis was dependent on ILC2s and signaling through IL4Rα. In the absence of IL4Rα or STAT6, IL-33-treated mice had less vascular leak and pulmonary edema, less endothelial activation, and reduced eotaxin production, cumulatively leading to a reduction of pathologic eosinophil migration into the lung parenchyma. These results offer a mouse model for use in future mechanistic studies of EGPA, and they suggest that IL-33, ILC2s, and IL4Rα signaling may be potential targets for further study and therapeutic targeting in patients with EGPA.

ANCA-Negative Churg-Strauss Syndrome Presenting as Bilateral Central Retinal Artery Occlusion: A Case Report

A 42-year-old man with undiagnosed Churg-Strauss syndrome (CSS) developed bilateral central retinal artery occlusion (CRAO). His medical history included bronchial asthma and irregular prednisolone usage but no atherosclerotic risk factors. At presentation, visual acuity (VA) was hand motion in the right eye and counting fingers in left eye. On fundoscopy, retinal whitening and a cherry red spot were observed in the right eye, while the fundus was normal in the left eye. After eyeball massage and systemic intraocular pressure lowering agents, his VA improved. On day 5 of treatment, he experienced right limb weakness and purpura on his right foot, and electromyography revealed mononeuritis multiplex. Laboratory tests indicated eosinophilia (52%). Based on the presence of hypereosinophilia, bronchial asthma, mononeuritis multiplex, vasculitis purpura, and sinusitis that was detected during etiological investigations, the patient was diagnosed as having CSS according to the American College of Rheumatology diagnostic criteria. Intravenous methylprednisolone 1 g/day was administrated for 3 consecutive days and 1 g cyclophosphamide was started and continued monthly for 6 months. Foot drop and vasculitic purpura improved after 7 days, but there was no further improvement in visual acuity. In conclusion, in the presence of bilateral CRAO and lack of atherosclerotic risk factors, CSS should be considered as a predisposing factor and investigations should be conducted accordingly.

Polyangiitis overlap syndrome: a novel presentation of microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis.

Polyangiitis overlap syndrome (POS) is a diagnostic term coined by Leavitt and Fauci that characterises patients with overlapping features of more than one vasculitis. Prior case studies of antineutrophil cytoplasmic antibodies (ANCA)-associated POS have only been published in patients with eosinophilic granulomatosis with polyangiitis (EGPA) and granulomatosis with polyangiitis alongside proteinase-3/cytoplasmic (C)-ANCA positivity. We present a case of a 60-year-old woman with dyspnoea, hemoptysis, positive perinuclear-ANCA and renal biopsy demonstrating evidence of microscopic polyangiitis. In addition, our patient also had asthma, mononeuritis multiplex, eosinophilia and migratory pulmonary infiltrates, thus fulfilling the criteria for EGPA. This novel case report suggests that POS is not limited to C-ANCA positivity and has variable presentations.

Pulmonary manifestations and outcomes in paediatric ANCA-associated vasculitis: a single-centre experience.

OBJECTIVES: ANCA-associated vasculitis (AAV) usually involves the renal and respiratory systems, but the paediatric literature on pulmonary manifestations and outcomes is limited. We aimed to describe pulmonary manifestations and outcomes after therapy in a cohort of paediatric AAV (pAAV) patients. METHODS: A retrospective chart review of all patients <19 years presenting to our institution with AAV between 1/2008 and 2/2018 was conducted. Patient demographics, clinical presentation, diagnostic testing, therapy and pulmonary outcomes over the first 3 years after presentation were evaluated. RESULTS: A total of 38 patients were included; all had ANCA positivity by immunofluorescence. A total of 23 had microscopic polyangiitis (MPA), 13 had granulomatosis with polyangiitis and 2 had eosinophilic granulomatosis with polyangiitis. A total of 30 (79%) had pulmonary manifestations, with cough (73%) and pulmonary haemorrhage (67%) being the most common. Abnormalities were noted in 82% of chest CT scans reviewed, with nodules and ground-glass opacities being the most common. At 6, 12 and 36 months follow-up, respectively, 61.8%, 39.4% and 29% of patients continued to show pulmonary manifestations. Five MPA patients with re-haemorrhage are described in detail. CONCLUSION: MPA was more common than granulomatosis with polyangiitis, with pulmonary involvement being common in both. MPA patients had more severe pulmonary manifestations. Chest CT revealed abnormal findings in a majority of cases. A subgroup of young MPA patients experienced repeat pulmonary haemorrhage. Treatment modality and response were comparable in different subtypes of AAV, except for this young MPA group. Additional prospective studies are needed to better understand the different phenotypes of pAAV.

Significance of PR3-ANCA positivity in eosinophilic granulomatosis with polyangiitis (Churg-Strauss).

OBJECTIVES: Only a third of patients with eosinophilic granulomatosis with polyangiitis (EGPA) are ANCA-positive, mainly directed against MPO. ANCA directed against PR3 are rarely found in EGPA. We aimed to examine the significance of PR3-ANCA in EGPA. METHODS: We set up a retrospective European multicentre cohort including 845 patients. Baseline characteristics and outcomes were analysed and compared according to ANCA status. RESULTS: ANCA status was available for 734 patients: 508 (69.2%) ANCA-negative, 210 (28.6%) MPO-ANCA and 16 (2.2%) PR3-ANCA. At baseline, PR3-ANCA patients, compared with those with MPO-ANCA and ANCA-negative, less frequently had active asthma (69% vs 91% and 93%, P = 0.003, respectively) and peripheral neuropathy (31% vs 71% and 47%, P < 0.0001), more frequently had cutaneous manifestations (63% vs 38% and 34%, P = 0.03) and pulmonary nodules (25% vs 10% and 8%, P = 0.046), and lower median eosinophil count (1450 vs 5400 and 3224/mm3, P < 0.0001). Vasculitis relapse-free survival was shorter for PR3-ANCA (hazard ratio 6.05, P = 0.005) and MPO-ANCA patients (hazard ratio 1.88, P = 0.0002) compared with ANCA-negative patients. CONCLUSION: PR3-ANCA EGPA patients differ from those with MPO-ANCA and negative ANCA, and share clinical features with granulomatosis with polyangiitis. This suggests that PR3-ANCA EGPA could be a particular form of PR3-ANCA-associated vasculitis.

Eosinophilic granulomatosis with polyangiitis presenting with myositis: case based review.

Eosinophilic granulomatosis with polyangitis (EGPA) is a systemic necrotizing small-vessel vasculitis that presents heterogeneously as a multi-organ disease. EGPA evolves through three phases: (1) prodromic phase with asthma, atopy and sinusitis, (2) eosinophilic phase characterized by peripheral eosinophilia and eosinophilic infiltration without necrosis, and (3) vasculitic phase involving organ damage. EGPA often presents with asthma, mononeuritis multiplex, lung infiltrates, sinusitis and constitutional symptoms. Although myalgias are common, EGPA rarely presents with true weakness with elevated creatinine kinase (CK). We describe a rare case of a patient presenting with eosinophilic myositis, who subsequently developed fulminant EGPA. The patient's diagnosis was supported by an initial clinical presentation of weakness and elevated CK, followed by fleeting pulmonary infiltrates and mononeuritis multiplex, peripheral eosinophilia, and strongly positive myeloperoxidase anti-cytoplasmic antibody (MPO-ANCA). Muscle biopsy revealed eosinophilic myositis. The patient responded well to high-dose glucocorticoids and cyclophosphamide with improved symptoms and biochemical markers. Based on our literature review, there are only seven similar cases reported of EGPA presenting with myositis and confirmatory muscle biopsies. There is significant heterogeneity in their clinical findings, histopathology and treatments that were used. Our case report and literature review highlights the importance of recognizing myositis as an initial presenting symptom of EGPA, providing an opportunity for early diagnosis and treatment to reduce risk of further disease progression and morbidity.

Pulmonary Eosinophilic Granulomatosis with Polyangiitis Has IgG4 Plasma Cells and Immunoregulatory Features.

The immunologic mechanisms promoting eosinophilic granulomatosis with polyangiitis (EGPA) are unclear. To characterize the mechanisms underlying pulmonary EGPA, we examined and compared EGPA paraffin-embedded lung biopsies with normal lung biopsies, using immunostaining, RNA sequencing, and RT-PCR. The results revealed novel type 2 as well as immuneregulatory features. These features included basophils and increased mast cell contents; increased immunostaining for tumor necrosis factor ligand superfamily member 14; sparse mast cell degranulation; numerous forkhead box protein P3 (FoxP3)+ regulatory T cells and IgG4 plasma cells; and abundant arachidonate 15-lipoxygenase and 25-hydroxyvitamin D-1 α hydroxylase, mitochondrial. Significantly decreased 15-hydroxyprostaglandin dehydrogenase [NAD(+)], which degrades eicosanoids, was observed in EGPA samples. In addition, there was significantly increased mRNA for chemokine (C-C motif) ligands 18 and 13 and major collagen genes, IgG4-rich immune complexes coating alveolar macrophages, and increased immunostaining for phosphorylated mothers against decapentaplegic homolog 2/SMAD2, suggesting transforming growth factor-ß activation. These findings suggest a novel self-promoting mechanism of activation of alveolar macrophages by arachidonate 15-lipoxygenase-derived eicosanoids to express chemokines that recruit a combined type 2/immunoregulatory immune response, which produces these eicosanoids. These results suggest that the pulmonary EGPA immune response resembles the immune response to a tissue-invasive parasite infection.

Differential clinicopathologic features of EGPA-associated neuropathy with and without ANCA.

OBJECTIVE: To investigate the clinicopathologic features of eosinophilic granulomatosis with polyangiitis (EGPA)-associated neuropathy with a focus on the presence or absence of anti-neutrophil cytoplasmic antibodies (ANCAs). METHODS: We examined the clinical features and pathologic findings of sural nerve biopsy specimens from 82 patients with EGPA-associated neuropathy. Of these patients, 32.9% were myeloperoxidase (MPO)-ANCA positive, and 67.1% were MPO-ANCA negative. PR3-ANCA was negative in all of 78 examined patients. RESULTS: Upper limb symptoms were more frequently reported as initial neuropathic manifestations in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (44.4% vs 14.6%, p < 0.01). The serum levels of C-reactive protein were significantly higher in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (p < 0.05). Sural nerve biopsy specimens showed findings suggestive of vasculitis (i.e., destruction of vascular structures) in epineurial vessels; these results were seen more frequently in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (p < 0.0001). Conversely, the numbers of eosinophils in the lumen of the epineurial vessels (p < 0.01) and epineurial vessels occluded by intraluminal eosinophils (p < 0.05) were higher in the MPO-ANCA-negative group than in the MPO-ANCA-positive group. Furthermore, the incidence of eosinophil infiltration in the endoneurium was higher in the MPO-ANCA-negative group than in the MPO-ANCA-positive group (p < 0.01). CONCLUSIONS: This study suggests that the pathogenesis of EGPA comprises at least 2 distinct mechanisms: ANCA-associated vasculitis resulting in ischemic effects and inflammation, which is prominent in MPO-ANCA-positive patients, and eosinophil-associated vascular occlusion leading to ischemia and eosinophil-associated tissue damage, which is conspicuous in MPO-ANCA-negative patients.

Eosinophilic Vasculitis.

PURPOSE OF REVIEW: Eosinophilic granulomatosis with polyangiitis (EGPA) represents a rare clinical entity, which is getting increasing attention and relevance in view of our better understanding and newer insights into its pathogenesis. Concomitantly better recognition and understanding of the immune pathophysiologic role of eosinophils provide a solid ground of their role on systemic inflammatory disorders and defense against infectious triggers, especially parasites. This review will focus on describing the physiopathology of eosinophils, as well as providing an in depth description of the natural history, clinical spectrum, and therapy of EGPA. RECENT FINDINGS: Several studies have aimed at finding useful biomarkers to monitor disease activity, and reported data have shown that eotaxin 3, IL25, IL33, and some eicosanoids to be promising options. Regarding therapeutic advances, recently published studies have revealed the efficacy of mepolizumab during induction and maintenance of EGPA. Recently published data confirmed earlier studies that the use of azathioprine during the induction phase is of no benefit during long-term follow-up. In addition, data from the REOVAS study, which uses rituximab, is still ongoing and apparently with promising results. Eosinophils are involved in several systemic inflammatory disorders, and recent gathered data provide support for their role in triggering EGPA. Better understanding of its pathophysiology should generate newer insights into the pathogenesis, biomarkers of disease activity, and therapeutic targets.

Eosinophilic granulomatosis with polyangiitis: the multifaceted spectrum of clinical manifestations at different stages of the disease.

Introduction: Eosinophilic granulomatosis with polyangiitis (EGPA) usually occurs in patients with late-onset asthma and sustained peripheral blood eosinophilia and classically presents with a clinical multifaceted spectrum of manifestations, which may vary at the different stages of the natural history of the disease.Areas covered: We reviewed EGPA clinical presentation, focusing on clinical manifestations at three different phases of the disease: 1/before the development of overt vasculitis, 2/at vasculitis diagnosis and 3/during the long-term follow-up. An update on current classification criteria and recent therapeutic advances has been provided as well.Expert opinion: Asthma, chronic rhinosinusitis and blood eosinophilia could anticipate the overt vasculitis for years. An atopic background may be present in a subset of patients (25-30%), while ANCA presence varies between 10 and 40%. Systemic vasculitis rapidly occurs and clinical features demonstrating vasculitis processes (neuropathy, purpura, scleritis, alveolar hemorrhage and glomerulonephritis) develop along with systemic symptoms (50%). After vasculitis resolution, asthma remains severe in up to 50% of patients and incidence of isolated-asthma and rhinosinus exacerbations remains constantly high. Different sets of classification criteria have been published so far, and DCVAS diagnostic criteria will be presented soon. Interleukin-5 blockers seem to be promising to control the disease and to spare corticosteroids.

ANCA-Associated Vasculitis: Core Curriculum 2020.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of disorders characterized by inflammation and destruction of small- and medium-sized blood vessels and the presence of circulating ANCA. Clinical disease phenotypes include granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis, and renal-limited vasculitis. Serologic classification of AAV into proteinase 3-ANCA disease and myeloperoxidase-ANCA disease correlates with a number of disease characteristics. AAV has a predilection for the kidney, with >75% of patients having renal involvement characterized by rapidly progressive glomerulonephritis. The cause and pathogenesis of AAV are multifactorial and influenced by genetics, environmental factors, and responses of the innate and adaptive immune system. Randomized controlled trials in the past 2 decades have refined the therapy of AAV and transformed AAV from a fatal disease to a chronic illness with relapsing course and associated morbidity. This article in AJKD's Core Curriculum in Nephrology series provides a detailed review of the epidemiology, pathogenesis, diagnosis, and advances in the management of AAV.