ANCA-associated vasculitis Medical Services in China

ANCA-associated vasculitis (AAV) is a group of rare, systemic autoimmune disorders characterized by inflammation and necrosis of small- to medium-sized blood vessels, primarily driven by autoantibodies against neutrophil cytoplasmic antigens (ANCAs). The three main clinical entities under this umbrella are granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). These diseases predominantly affect the kidneys, lungs, upper airways, skin, nerves, and joints. Pathogenesis centers on dysregulated neutrophil activation: ANCAs—most commonly targeting proteinase 3 (PR3-ANCA in GPA) or myeloperoxidase (MPO-ANCA in MPA and EGPA)—bind to primed neutrophils, triggering uncontrolled degranulation, reactive oxygen species release, and endothelial injury. This cascade leads to pauci-immune necrotizing glomerulonephritis (a hallmark renal lesion), pulmonary capillaritis, and granulomatous inflammation in GPA. Genetic susceptibility (e.g., HLA-DQ variants, PRTN3 polymorphisms), environmental triggers (e.g., silica exposure, chronic nasal Staphylococcus aureus colonization, certain drugs like hydralazine or propylthiouracil), and epigenetic dysregulation contribute to disease onset. Epidemiologically, AAV affects approximately 10–20 new cases per million people annually worldwide, with prevalence estimated at 50–250 per million. Incidence rises sharply after age 50, peaking in the seventh decade; males and females are equally affected overall, though GPA shows slight male predominance. In China, AAV is increasingly recognized but likely underdiagnosed due to nonspecific early symptoms and limited ANCA testing access outside major centers. Key risk factors include older age, chronic sinusitis or asthma (especially in EGPA), occupational silica exposure, smoking, and certain infections. Renal involvement—present in up to 80% of GPA and MPA cases—often manifests as rapidly progressive glomerulonephritis (RPGN), leading to acute kidney injury and, if untreated, end-stage kidney disease requiring dialysis or transplantation. Beyond renal morbidity, patients frequently experience debilitating fatigue, arthralgias, neuropathy, pulmonary hemorrhage, and persistent upper respiratory tract damage. Quality of life is profoundly impacted: over 60% report moderate-to-severe impairment in physical functioning, role limitations, and mental health; depression and anxiety rates exceed population norms by 3–4 fold. Chronic immunosuppression increases infection risk and long-term cardiovascular morbidity, while treatment-related side effects—including osteoporosis, diabetes, cataracts, and malignancy—further erode well-being. Early diagnosis via ANCA serology (ELISA + IIF), renal biopsy (showing pauci-immune crescentic GN), and imaging (e.g., CT chest/sinus) is critical. Delayed recognition remains common, contributing to irreversible organ damage and higher mortality—5-year survival ranges from 70% to 85%, heavily dependent on timely intervention and sustained remission maintenance.

ANCA-associated vasculitis (AAV) comprises a group of systemic autoimmune disorders characterized by necrotizing inflammation of small- to medium-sized blood vessels, pauci-immune glomerulonephritis, and the presence of antineutrophil cytoplasmic antibodies (ANCAs). The three primary clinical entities are granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). While the precise etiology remains incompletely understood, AAV is widely regarded as an immune-mediated disease driven by dysregulated neutrophil activation, aberrant T- and B-cell responses, and loss of self-tolerance to neutrophil-derived antigens—primarily proteinase 3 (PR3) in GPA and myeloperoxidase (MPO) in MPA and EGPA.

The fundamental pathogenic mechanism involves autoantibodies (ANCAs) binding to PR3 or MPO expressed on the surface of primed neutrophils, triggering uncontrolled neutrophil degranulation, reactive oxygen species release, and neutrophil extracellular trap (NET) formation. This cascade incites endothelial injury, vascular inflammation, and subsequent organ damage—most critically in the kidneys (focal segmental necrotizing glomerulonephritis with crescent formation), lungs (pulmonary capillaritis), upper airways, skin, and peripheral nerves.

No single exogenous cause has been identified; rather, AAV arises from complex interactions among genetic susceptibility, environmental exposures, and immunoregulatory perturbations. Genetic factors confer substantial risk: genome-wide association studies (GWAS) have robustly linked HLA-DP and HLA-DQ alleles with PR3-ANCA positivity, particularly *HLA-DPB1* rs20417 and *HLA-DQA1* rs2857096. Polymorphisms in non-HLA genes—including *PRTN3* (encoding PR3), *SERPINA1* (alpha-1-antitrypsin, a natural PR3 inhibitor), *PTPN22*, and *CTLA4*—modulate antigen processing, neutrophil apoptosis, and T-cell checkpoint regulation. Notably, *SERPINA1* deficiency (e.g., PiZ or PiS variants) increases PR3-ANCA prevalence and disease severity, likely due to impaired PR3 clearance and prolonged antigen exposure.

Environmental triggers play a critical role in disease initiation and relapse. Chronic nasal carriage of *Staphylococcus aureus* is strongly associated with GPA relapse; prospective trials demonstrate that antibiotic prophylaxis (e.g., co-trimoxazole) significantly reduces relapse rates, implicating bacterial superantigen-driven T-cell activation and molecular mimicry. Silica dust exposure—common in mining, construction, and agriculture—is an established occupational risk factor for MPA and renal-limited vasculitis, potentially via macrophage activation, inflammasome stimulation (NLRP3), and enhanced autoantigen presentation. Other implicated exposures include chronic inhalational irritants (e.g., tobacco smoke, solvents), certain medications (e.g., propylthiouracil, hydralazine, minocycline), and viral infections (e.g., hepatitis B/C, HIV), though evidence for direct causality remains limited. Seasonal variation and geographic clustering suggest additional unidentified environmental cofactors.

Demographic and clinical risk factors include advanced age (peak incidence 60–70 years), male sex (particularly for GPA and renal involvement), and preexisting chronic inflammatory conditions such as chronic rhinosinusitis (especially with nasal polyps in GPA) or asthma/eosinophilia (in EGPA). Renal impairment at diagnosis—reflected by elevated serum creatinine, reduced eGFR, or histologic crescentic glomerulonephritis—is the strongest predictor of end-stage kidney disease (ESKD) and mortality. Hypertension, proteinuria >1 g/day, and ANCA titer magnitude (particularly PR3-ANCA) correlate with renal flare risk. Importantly, while ANCAs are central to pathogenesis, their presence alone does not equate to active disease; persistent seropositivity post-treatment may indicate subclinical immune dysregulation but requires clinical and histopathologic correlation.

In summary, AAV is a multifactorial disorder arising from inherited immune dysregulation interacting with environmental insults that breach tolerance to neutrophil antigens. Understanding these interrelationships informs risk stratification, monitoring strategies, and emerging targeted therapies—including B-cell depletion (rituximab), complement inhibition (avacopan), and BAFF blockade—aimed at restoring immune homeostasis and preserving renal function.

ANCA-associated vasculitis (AAV) comprises a group of systemic, necrotizing small-vessel vasculitides characterized by the presence of antineutrophil cytoplasmic antibodies (ANCAs) and pauci-immune histopathology—meaning minimal or absent immunoglobulin and complement deposition on renal biopsy. The three primary clinical entities within AAV are granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). In nephrology practice, renal involvement is a hallmark feature and often the presenting or dominant manifestation, particularly in GPA and MPA; EGPA more commonly presents with asthma and eosinophilia but may develop glomerulonephritis in up to 30–40% of cases. Early symptoms are frequently nonspecific and insidious, contributing to diagnostic delay. Patients commonly report constitutional symptoms including persistent fatigue, low-grade fever, weight loss (>5% body weight over 6 months), and myalgias or arthralgias—often migratory and non-deforming. Upper respiratory tract manifestations may precede renal disease by weeks to months: chronic sinusitis, nasal crusting or epistaxis, saddle-nose deformity (suggestive of GPA), otitis media, or sensorineural hearing loss. Cough, dyspnea, or hemoptysis may signal pulmonary capillaritis or nodular infiltrates. Cutaneous manifestations—including palpable purpura (most common), livedo reticularis, digital infarcts, or ulcers—occur in ~40–60% of patients and reflect cutaneous small-vessel inflammation. Neurologic symptoms such as mononeuritis multiplex or peripheral neuropathy (especially in EGPA) may also herald disease onset.

Typical symptoms reflect active, organ-specific vasculitic injury. Renal involvement—present in >75% of GPA and MPA cases—is typically pauci-immune crescentic glomerulonephritis (CrGN), manifesting as rapidly progressive glomerulonephritis (RPGN). Patients present with hematuria (microscopic or macroscopic), proteinuria (usually subnephrotic, <3.5 g/day), red blood cell casts on urinalysis, and an acute or subacute rise in serum creatinine. Hypertension may be present but is less prominent than in other glomerulopathies due to preserved renal perfusion early in disease. Pulmonary-renal syndrome—simultaneous alveolar hemorrhage and RPGN—is a medical emergency, presenting with dyspnea, cough, hypoxemia, diffuse alveolar opacities on chest imaging, and falling hemoglobin without overt bleeding. ENT involvement includes destructive sinonasal disease, orbital pseudotumor, or scleritis. In EGPA, asthma exacerbation, new-onset or worsening allergic rhinitis, and marked peripheral eosinophilia (>1.5 × 10⁹/L) are cardinal features.

Accompanying symptoms reflect systemic inflammation and immune dysregulation. Mild normocytic, normochromic anemia is nearly universal, driven by chronic disease and renal impairment. Thrombocytosis may occur in active disease. Elevated acute-phase reactants—C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)—are typical but nonspecific. Hypocomplementemia is notably absent, distinguishing AAV from immune-complex-mediated vasculitides like lupus nephritis or cryoglobulinemic vasculitis. Ocular involvement beyond scleritis includes conjunctivitis, episcleritis, or optic neuritis. Gastrointestinal symptoms—abdominal pain, diarrhea, or gastrointestinal bleeding—may arise from mesenteric vasculitis but are less frequent than renal or pulmonary manifestations.

Complications stem from both uncontrolled vasculitis and iatrogenic effects of immunosuppression. End-stage kidney disease (ESKD) develops in 10–25% of patients with severe CrGN, especially if diagnosis or treatment is delayed beyond 3 months from symptom onset. Pulmonary fibrosis may follow recurrent alveolar hemorrhage or chronic interstitial inflammation. Cardiovascular complications include accelerated atherosclerosis, myocardial infarction, and heart failure—partly attributable to chronic inflammation and corticosteroid use. Infections—particularly Pneumocystis jirovecii pneumonia (PJP), herpes zoster, and bacterial sepsis—are leading causes of early mortality. Malignancy risk, especially urothelial carcinoma (associated with cyclophosphamide exposure), lymphoma, and skin cancers, warrants long-term surveillance. Relapses occur in 30–50% of patients over 5 years, most commonly within the first 2 years, and may involve new or recurrent organ systems.

Diagnosis integrates clinical assessment, serologic testing, imaging, and histopathology. ANCA testing is central: cytoplasmic ANCA (c-ANCA) with proteinase 3 (PR3) specificity strongly supports GPA (sensitivity ~85–90%, specificity >95% in active disease); perinuclear ANCA (p-ANCA) with myeloperoxidase (MPO) specificity is associated with MPA and renal-limited vasculitis (sensitivity ~60–75%, specificity ~90%). ELISA for PR3- and MPO-ANCA is preferred over indirect immunofluorescence alone due to superior specificity. Urinalysis consistently reveals active sediment: dysmorphic RBCs, RBC casts, and mild proteinuria. Serum creatinine and estimated glomerular filtration rate (eGFR) quantify renal dysfunction. Chest imaging—high-resolution CT—detects nodules, ground-glass opacities, or cavitation in GPA; patchy consolidations or septal thickening in MPA; or bronchial wall thickening and mucoid impaction in EGPA. Sinus CT demonstrates mucosal thickening, polyps, or bony destruction. Kidney biopsy remains the gold standard for confirming pauci-immune CrGN: light microscopy shows focal, segmental, necrotizing glomerulonephritis with cellular crescents; immunofluorescence reveals absent or trace IgG/IgA/IgM and C3; electron microscopy excludes electron-dense deposits. Lung biopsy is rarely required unless diagnosis remains uncertain after noninvasive evaluation.

Differential diagnosis is broad and must exclude mimics. Immune-complex vasculitides—systemic lupus erythematosus (SLE), IgA vasculitis (Henoch-Schönlein purpura), and cryoglobulinemic vasculitis—typically show positive immunofluorescence and hypocomplementemia. Anti-glomerular basement membrane (anti-GBM) disease presents similarly with RPGN and pulmonary hemorrhage but demonstrates linear IgG staining on renal biopsy and circulating anti-GBM antibodies; it may coexist with ANCA (‘double-positive’ disease), portending worse renal outcomes. Infectious endocarditis can mimic vasculitis via embolic phenomena and immune complex deposition—blood cultures and echocardiography are essential. Malignancy-associated paraneoplastic syndromes (e.g., renal cell carcinoma, lymphoma) may cause glomerulonephritis or vasculitic-like symptoms; age-appropriate cancer screening is mandatory. Drug-induced vasculitis (e.g., propylthiouracil, hydralazine, minocycline) must be excluded by detailed medication history; drug-induced ANCA is often MPO-positive but rarely causes severe renal disease. Finally, other primary small-vessel vasculitides—such as Behçet’s disease or isolated CNS vasculitis—lack ANCA positivity and exhibit distinct clinical patterns. Accurate diagnosis hinges on multidisciplinary integration of nephrology, rheumatology, pulmonology, and pathology expertise.

ANCA-associated vasculitis (AAV) is a group of systemic autoimmune disorders characterized by necrotizing inflammation of small- to medium-sized blood vessels, strongly associated with antineutrophil cytoplasmic antibodies (ANCA). The three primary clinical phenotypes—granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA)—frequently involve the kidneys, manifesting as pauci-immune crescentic glomerulonephritis. As such, nephrology departments play a central role in diagnosis, risk stratification, and longitudinal management. Treatment is stratified by disease severity (limited vs. severe/organ-threatening), renal function at presentation, and histopathological findings on kidney biopsy.

Conservative treatment forms the essential foundation of AAV management and must be initiated concurrently with immunosuppression. This includes strict blood pressure control targeting <130/80 mmHg using renin-angiotensin-aldosterone system inhibitors (e.g., ACE inhibitors or ARBs), which confer dual benefits of antiproteinuric and renoprotective effects. Fluid and electrolyte balance must be meticulously monitored, especially in patients with acute kidney injury (AKI) or rapidly progressive glomerulonephritis (RPGN); diuretics may be required for volume overload, while sodium restriction (<2 g/day) and potassium monitoring are critical in advanced chronic kidney disease (CKD). Nutritional support is vital: a low-sodium, moderate-protein (0.8–1.0 g/kg/day) diet helps mitigate glomerular hyperfiltration and uremic complications without compromising immune competence. Smoking cessation is non-negotiable, given its strong association with disease relapse and reduced treatment response. Vaccination status must be reviewed and updated—particularly pneumococcal, influenza, hepatitis B, and SARS-CoV-2 vaccines—prior to initiating immunosuppression, as live vaccines are contraindicated during active therapy.

Pharmacotherapy remains the cornerstone of AAV treatment and follows a biphasic strategy: induction and maintenance. For severe disease (e.g., serum creatinine >300 µmol/L, >50% crescents on biopsy, or pulmonary-renal syndrome), induction therapy consists of high-dose glucocorticoids (prednisone 1 mg/kg/day tapered over 3–6 months) combined with either cyclophosphamide (oral 2 mg/kg/day or IV pulse regimens) or rituximab (375 mg/m² weekly ×4 or 1000 mg ×2 doses two weeks apart). Rituximab is now preferred for both GPA and MPA in most guidelines—including KDIGO 2021—due to superior safety profile, particularly regarding gonadal toxicity and malignancy risk. For EGPA with predominant asthma/eosinophilia and no major organ involvement, mepolizumab or benralizumab (anti-IL-5 biologics) may be considered adjunctively, though evidence remains limited. Maintenance therapy begins after remission is achieved (typically within 3–6 months) and continues for ≥24–48 months. Azathioprine (2 mg/kg/day) or mycophenolate mofetil (1–1.5 g twice daily) are standard options; rituximab (500–1000 mg every 6 months) is increasingly used for sustained remission, especially in relapsing disease. Plasma exchange (PLEX) is indicated for severe RPGN (serum creatinine >500 µmol/L or dialysis dependence) or diffuse alveolar hemorrhage, with protocols typically involving 7 sessions over 14 days. Adjunctive therapies include prophylaxis against Pneumocystis jirovecii pneumonia (e.g., trimethoprim-sulfamethoxazole), calcium/vitamin D supplementation, and bisphosphonates for steroid-induced osteoporosis.

Surgical intervention is rarely indicated in AAV but may be necessary in specific complications. End-stage kidney disease (ESKD) resulting from irreversible glomerulosclerosis and interstitial fibrosis requires renal replacement therapy—either hemodialysis, peritoneal dialysis, or kidney transplantation. Transplantation is feasible once disease has been quiescent for ≥12–24 months and ANCA titers are persistently negative; recurrence rates post-transplant are low (<5% at 5 years) but necessitate vigilant monitoring. Sinus surgery may be performed in GPA patients with refractory sinonasal granulomatous disease unresponsive to medical therapy, improving drainage and reducing infection burden. Tracheal stenosis—a late complication of GPA—may require endoscopic dilation or airway stenting, and in severe cases, surgical resection with reconstruction. Pulmonary nodules or cavitary lesions that fail to regress or demonstrate atypical growth patterns warrant biopsy to exclude malignancy or infection, though surgical resection is seldom first-line.

China offers distinct advantages in the multidisciplinary management of AAV. First, integrated nephrology-rheumatology-immunology centers—such as those at Peking University First Hospital and Shanghai Renji Hospital—employ standardized, protocol-driven care pathways aligned with international guidelines yet adapted to regional epidemiology and pharmacogenomic profiles (e.g., optimized cyclophosphamide dosing based on CYP2B6 polymorphisms). Second, China’s national rare disease registry and centralized biobanks facilitate rapid access to real-world data, enabling timely identification of treatment responders and early detection of relapse via serial ANCA monitoring and urinary biomarkers (e.g., CD163+ monocytes, NGAL). Third, cost-effective biosimilar rituximab and domestically manufactured mycophenolate formulations significantly improve treatment accessibility, particularly in tier-2 and tier-3 cities. Fourth, traditional Chinese medicine (TCM) adjuncts—such as Huangqi (Astragalus membranaceus) and Danshen (Salvia miltiorrhiza)—are rigorously studied in randomized controlled trials for their anti-fibrotic and endothelial-stabilizing properties; several TCM formulas have demonstrated additive benefit in reducing proteinuria and delaying CKD progression when co-administered with standard immunosuppression, under strict pharmacovigilance oversight.

Recovery and long-term follow-up demand structured patient engagement. Patients should undergo quarterly nephrology visits for assessment of eGFR, urinalysis, ANCA titers, and complement levels; annual chest CT and ENT evaluation are recommended for GPA. Home blood pressure and weight monitoring empower early recognition of fluid retention or hypertension flare. Physical rehabilitation—including graded aerobic exercise and resistance training—is encouraged to counteract steroid-induced myopathy and improve cardiovascular fitness. Psychosocial support is integral: depression and anxiety affect >30% of AAV survivors, and dedicated counseling services are embedded in major Chinese nephrology centers. Finally, fertility preservation counseling should be offered prior to cyclophosphamide initiation, and pregnancy planning must occur only after ≥12 months of stable remission and normalized renal function. With contemporary protocols, 5-year patient survival exceeds 85%, and renal survival surpasses 75% in those presenting with preserved baseline eGFR—underscoring the importance of early diagnosis, precision immunosuppression, and lifelong nephrology stewardship.