anca associated vasculitis

ANCA-associated vasculitis is a group of rare autoimmune diseases in which the body’s own antibodies attack small blood vessels, causing inflammation that can damage the kidneys, lungs, nerves, and other organs. The antibodies in question, called antineutrophil cytoplasmic antibodies (ANCA), latch onto proteins inside white blood cells and set off an immune chain reaction that eats away at blood vessel walls. Left untreated, the disease can be life-threatening, but modern treatments have transformed it from a near-certain fatal diagnosis into a manageable chronic condition for most people.

Three Diseases Under One Umbrella

ANCA-associated vasculitis (AAV) is not one disease but three, each with overlapping features but distinct patterns of organ involvement. Granulomatosis with polyangiitis (GPA, formerly called Wegener’s) tends to target the upper airways, lungs, and kidneys, often forming inflammatory nodules or cavities in the lungs. Microscopic polyangiitis (MPA) hits the kidneys and lungs too, but its hallmark lung finding is scarring (interstitial fibrosis) rather than nodules. Eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss syndrome) stands apart because it involves asthma, nasal polyps, and elevated levels of eosinophils, a type of white blood cell linked to allergic responses.¹

The 2022 classification criteria developed jointly by the American College of Rheumatology and the European Alliance of Associations for Rheumatology use weighted scoring that incorporates imaging, lab findings, and biopsy results to separate the three subtypes. An increasingly influential approach goes even simpler: classifying patients by which protein their ANCA targets. People whose antibodies attack proteinase 3 (PR3-ANCA) tend to behave clinically like GPA patients, while those whose antibodies attack myeloperoxidase (MPO-ANCA) tend to look like MPA. A retrospective analysis found that classifying patients by ANCA type alone showed substantial agreement with the full 2022 criteria for both GPA and MPA. EGPA classification stayed consistent regardless of which method was used, since ANCA specificity matters less for that subtype.²

What Happens Inside the Blood Vessels

The core problem in AAV is that ANCA antibodies activate neutrophils, the immune system’s rapid-response cells. In healthy people, neutrophils patrol the bloodstream and destroy bacteria. In AAV, ANCA binds to neutrophils and triggers them to release their destructive contents directly against the walls of small blood vessels. This causes inflammation, tissue death, and organ damage.

One important mechanism involves structures called neutrophil extracellular traps (NETs). These are web-like tangles of DNA and toxic proteins that neutrophils normally cast out to ensnare bacteria. In AAV, ANCA-stimulated neutrophils throw out NETs excessively, and those NETs damage the cells lining blood vessels.³ Research has shown that this NET release happens through a specific form of cell death called necroptosis, and that the NETs directly injure endothelial cells in lab experiments.⁴

The complement system, another arm of the immune response, also fuels the fire. In patients with active AAV, blood levels of complement components like C3a, C5a, and the membrane attack complex are markedly elevated compared to healthy controls. When patients reach remission with treatment, levels of C3a, C5a, and factor B drop significantly.⁵ This complement involvement has become clinically relevant because a newer drug, avacopan, works by blocking the C5a receptor.

Who Gets It and Why

No single cause explains AAV. Like many autoimmune diseases, it appears to arise from a collision of genetic predisposition and environmental triggers. A large genome-wide study found that PR3-ANCA vasculitis is strongly linked to certain immune-system genes, particularly HLA-DP and genes encoding the target proteins themselves (proteinase 3 and its inhibitor, alpha-1 antitrypsin). MPO-ANCA vasculitis, by contrast, was associated with a different immune gene region, HLA-DQ.⁶ A Scandinavian study confirmed and refined these associations, linking PR3-AAV to specific variants at HLA-DPB1 and MPO-AAV to HLA-DRB1.⁷ The genetic picture strongly supports the idea that PR3-ANCA and MPO-ANCA diseases are fundamentally distinct conditions, not just variations on a single theme.

On the environmental side, silica dust exposure roughly doubles the odds of developing AAV. A systematic review and meta-analysis found that people with a history of silica exposure had about two and a half times the risk of AAV compared to unexposed individuals, with comparable elevations for both GPA and MPA.⁸ Occupations involving mining, sandblasting, and construction carry the highest exposure risk.

Certain medications can also trigger AAV. Hydralazine, a blood pressure drug, is the best-studied pharmaceutical culprit. Researchers recently uncovered a mechanism: hydralazine chemically modifies myeloperoxidase, changing its shape enough that the immune system treats it as foreign and produces antibodies against it. Patients with hydralazine-associated vasculitis had elevated antibodies with heightened affinity for the drug-modified form of the protein, and the modified protein was pathogenic in a mouse model.⁹

Organs Under Attack

The kidneys are the organ most commonly and dangerously affected by AAV. The characteristic kidney lesion is a form of inflammation in the tiny blood-filtering units called glomeruli, producing what pathologists describe as pauci-immune necrotizing and crescentic glomerulonephritis. In plain terms, the filters become inflamed, start dying, and form crescent-shaped scars that choke off their function.¹⁰ If enough of these filtering units are destroyed before treatment begins, kidney function may not fully recover.

Lung involvement takes different forms depending on the subtype and ANCA type. In GPA and C-ANCA-positive patients, alveolar hemorrhage (bleeding into the air sacs) is more common. In MPO-ANCA/P-ANCA-positive patients, interstitial lung disease, a progressive scarring of lung tissue, predominates.¹¹ The upper airways are frequently involved in GPA, with symptoms like chronic sinusitis, nosebleeds, and nasal crusting. Severe cases can erode the nasal cartilage, leading to a characteristic “saddle nose” deformity.

Nerves, eyes, skin, and joints can all be targeted too. Peripheral neuropathy, in which damaged blood vessels starve the nerves of oxygen, often shows up as numbness, tingling, or weakness in the hands and feet. Skin involvement ranges from purplish spots (purpura) to painful ulcers.

Diagnosis and ANCA Testing

Testing for ANCA has historically involved two steps: first, a screening test using indirect immunofluorescence (IIF), and then a confirmatory test using an antigen-specific immunoassay to determine whether the antibodies target PR3 or MPO. A large European evaluation found that the antigen-specific immunoassays alone performed well enough to distinguish AAV from other conditions, challenging the need for dual testing of every sample.¹² This matters practically because IIF results can vary substantially between laboratories, whereas immunoassays tend to be more standardized.

A comparative study confirmed the gap: IIF flagged roughly 18% of tested samples as ANCA-positive, while the immunoassay flagged about 12%. Using IIF as the benchmark, the immunoassay had high specificity (about 99%) but more modest sensitivity (about 61%), meaning it missed some positives that IIF caught.¹³ In practice, many centers now use the antigen-specific assay as a first-line screen, reserving IIF for ambiguous cases. No blood test alone clinches the diagnosis; biopsy of an affected organ remains important in many cases to confirm vasculitis and guide treatment.

Inducing Remission

For decades, the standard way to beat back active AAV was cyclophosphamide, a potent immunosuppressant originally developed as a cancer drug, combined with high-dose glucocorticoids. This regimen works, but at a cost: cyclophosphamide raises the risk of infections, infertility, bladder problems, and future cancers with prolonged use.

The RAVE trial, published in 2010, changed the landscape. It showed that rituximab, an antibody that depletes B cells (the immune cells that produce ANCA), was at least as effective as cyclophosphamide for inducing remission. About 64% of patients in the rituximab group achieved complete remission by six months, compared with 53% in the cyclophosphamide group. For patients who were experiencing a disease relapse rather than a first flare, rituximab was clearly superior, with 67% achieving remission versus 42% on cyclophosphamide.¹⁴ Rituximab was also effective in patients with severe kidney disease or lung hemorrhage. Longer follow-up confirmed that rituximab’s advantage in relapsing disease held through 12 months but narrowed by 18 months, as B cells returned in most patients who did not receive additional rituximab doses.¹⁵

Rituximab is now the preferred induction agent for most patients, especially those with relapsing disease. Cyclophosphamide remains an option, particularly in settings where rituximab is unavailable or in certain severe presentations.

Keeping the Disease Quiet

Getting AAV into remission is only half the battle. Relapse is common, and the choice of ANCA target matters here. Patients with PR3-ANCA are almost twice as likely to relapse as those with MPO-ANCA.¹⁶ This makes effective maintenance therapy essential.

The MAINRITSAN trial compared rituximab to azathioprine (a traditional oral immunosuppressant) for maintaining remission. At 28 months, major relapse had occurred in 29% of patients on azathioprine but only 5% of those on rituximab.¹⁷ A follow-up trial (MAINRITSAN3) tested whether continuing rituximab beyond the initial maintenance period further reduced relapse. Relapse-free survival at 28 months was 96% in the extended-rituximab group compared with 74% in the group that stopped rituximab and switched to placebo.¹⁸ These results have pushed practice toward longer courses of rituximab maintenance, though the optimal total duration remains an active question.

Reducing Steroid Dependence

High-dose glucocorticoids (prednisone and its relatives) have been part of AAV treatment from the beginning, but they bring a roster of side effects: weight gain, diabetes, osteoporosis, infections, cataracts, and mood disturbances. Avacopan, a pill that blocks the receptor for complement component C5a, was developed specifically to reduce or eliminate steroid use in AAV.

An early-phase trial demonstrated that avacopan could replace prednisone entirely without compromising effectiveness. About 81% of patients on avacopan alone achieved a clinical response at 12 weeks, compared with 70% on standard prednisone, meeting the threshold for noninferiority.¹⁹ The larger phase 3 ADVOCATE trial then compared avacopan to a prednisone taper, with both groups also receiving rituximab or cyclophosphamide. At 26 weeks, remission rates were similar (about 72% with avacopan versus 70% with prednisone). The real separation came at 52 weeks: roughly 66% of avacopan-treated patients maintained sustained remission compared to about 55% on prednisone, a statistically significant difference.²⁰ Avacopan has since been approved in multiple countries and represents the first genuinely new mechanism of action for AAV treatment in decades.

The Plasma Exchange Debate

Plasma exchange, which physically removes ANCA and other inflammatory molecules from the blood, has long been used for the most severe AAV presentations, especially when the kidneys are failing rapidly. The rationale is intuitive: strip out the antibodies causing the damage. But the evidence is more complicated than the logic.

The PEXIVAS trial, the largest study of plasma exchange in AAV, found no significant benefit for the combined outcome of death or end-stage kidney disease. About 28% of patients who received plasma exchange hit that endpoint, compared with 31% in the control group, a difference that could easily have been due to chance.²¹ A secondary analysis did find that plasma exchange improved kidney function in the short term, with a meaningful bump in filtration rate at two, four, and eight weeks, but the advantage disappeared at later time points.²²

An updated systematic review pooling data from multiple trials concluded that plasma exchange reduces the risk of end-stage kidney disease at 12 months but does not affect mortality. It also increases the risk of serious infections.²³ The current consensus is nuanced: plasma exchange is no longer considered routine for severe AAV, but it may still have a role in patients with the most advanced kidney damage at presentation, where any short-term preservation of function could keep someone off dialysis.

EGPA and the Role of Mepolizumab

EGPA behaves differently enough from GPA and MPA that it often requires its own treatment strategy. Because eosinophils drive much of the damage, therapies targeting interleukin-5 (IL-5), a signaling molecule that fuels eosinophil growth and survival, have proven effective. Mepolizumab, an antibody that blocks IL-5, was tested in the phase 3 MIRRA trial. Patients receiving mepolizumab were far more likely to achieve sustained remission: about 32% were in remission at both 36 and 48 weeks compared with just 3% on placebo. The relapse rate was cut in half.²⁴ An important practical benefit was that mepolizumab allowed patients to reduce their daily steroid doses, easing the burden of long-term glucocorticoid side effects.

Real-world experience from a European multicenter study confirmed the trial findings, and long-term follow-up has shown that mepolizumab remains well tolerated over years of continuous use, with sustained reductions in steroid requirements.²⁵ For EGPA patients who struggle with recurrent flares or who cannot tolerate steroids, mepolizumab has become a standard option.

Long-Term Damage Accumulates

Even when treatment controls the vasculitis itself, many patients accumulate organ damage over time, from the disease, from its treatment, or from both. A study tracking over 600 European patients found that about a third already had at least one item of permanent damage at the time of diagnosis. After an average of about seven years, only 8% had escaped damage entirely, and a third had five or more items of damage. The most common problems were kidney impairment, high blood pressure, nasal crusting, hearing loss, and nerve damage. Treatment-related damage was widespread too: hypertension affected about 42%, osteoporosis about 14%, cancer about 13%, and diabetes about 10%.²⁶

These numbers underscore why the field is so focused on steroid-sparing approaches and why relapse prevention matters as much as initial remission. Each flare risks additional irreversible damage, and every month on high-dose steroids adds treatment-related injury. The goal of modern care has shifted from simply suppressing the disease to doing so with the least cumulative harm.

AAV in Children

AAV is rare in children, but when it occurs, it tends to present aggressively. A French study of pediatric patients found that ear, nose, and throat involvement was frequent (about 46%) and often more severe than what is typically seen in adults. Kidney outcomes were poor: roughly 55% of children had chronic kidney disease within a year of diagnosis, and mortality remained low at about 6.5%.²⁷

A larger international study of 85 children with kidney involvement found that about 29% progressed to kidney failure, and this typically happened early in the disease course. Children whose kidney biopsies showed extensive scarring had dramatically worse outcomes than those with more focal disease.²⁸ Treatment in children largely follows adult protocols, with cyclophosphamide still widely used for induction in pediatric settings, though rituximab use is growing. The challenge is that children face decades of disease management and cumulative exposure to immunosuppressive drugs, making early and effective control even more critical.

Staphylococcus aureus and Relapse Risk in GPA

An old clinical observation holds that people with GPA who carry the bacterium Staphylococcus aureus in their noses tend to relapse more often. Some clinicians have prescribed antibiotics (particularly trimethoprim-sulfamethoxazole) to eradicate the bacteria. The evidence, however, is mixed and somewhat confusing.

A Dutch cohort study found that among all AAV patients, carrying S. aureus in the nose did not significantly increase the risk of systemic relapse, and antibiotic treatment to eradicate the bacteria did not reduce disease activity.²⁹ But the picture changes when you zoom in on a specific subset. A separate study of newly diagnosed patients found that chronic nasal carriers who had GPA, specifically generalized GPA with serious organ involvement, relapsed about four times as often as non-carriers.³⁰ The prevailing theory is that S. aureus may stimulate the immune system locally in the nasal passages, feeding the inflammatory loop in patients with GPA-type disease, but proving causation has been elusive.

Urine as a Window Into Relapse

Predicting when AAV will flare is one of the field’s biggest unmet needs. Rising ANCA titers sometimes signal an oncoming relapse, but their track record as a standalone predictor is mediocre. A more promising approach looks at what is being shed into the urine. A study of over 100 patients found that the presence of certain immune cells (CD4-positive T cells) in urine was a strong predictor of kidney relapse within six months, with a specificity of about 98% and sensitivity of 60%. This outperformed ANCA titers, protein in the urine, and blood in the urine as relapse predictors.³¹ If validated in larger studies, this kind of biomarker could allow doctors to intervene before a full relapse develops, potentially sparing patients from another round of aggressive treatment and the organ damage that comes with uncontrolled inflammation.