Renal Vasculitis Diagnosis and Management

Definition and Classification

• Renal vasculitis is characterized by necrotizing inflammation of small blood vessels in the kidneys, typically presenting as rapidly progressive glomerulonephritis with hematuria, proteinuria, and declining kidney function, according to the Kidney International guidelines 1, 2
• The kidney lesion is characterized by pauci-immune focal and segmental necrotizing and crescentic glomerulonephritis (NCGN), as reported by Kidney International 1, 2
• Eosinophilic granulomatosis with polyangiitis (EGPA) is a type of renal vasculitis, as described in Kidney International 1, 3

Pathophysiology and Clinical Features

• About 90% of patients with small-vessel vasculitis affecting the kidneys have ANCA, directed primarily against myeloperoxidase (MPO) or proteinase 3 (PR3) neutrophil proteins, according to Kidney International 1, 2
• Clinical manifestations include microscopic hematuria with dysmorphic red blood cells and red cell casts, as reported by Kidney International 4
• Moderate proteinuria (1-3 g/day) is a common clinical feature, as described in Kidney International 2
• Rapidly declining glomerular filtration rate (GFR) over days to weeks is a characteristic of renal vasculitis, according to Kidney International 1, 3

Diagnosis

• Diagnosis relies on a combination of clinical findings, laboratory tests, and kidney biopsy, as reported by Kidney International 1, 2, 4, 5
• High-quality antigen-specific immunoassays are the preferred screening method for MPO- and PR3-ANCA, according to Kidney International 1
• Kidney biopsy remains the gold standard for diagnosis with a diagnostic yield as high as 91.5% in GPA, as described in Kidney International 2, 4

Treatment

• Plasma exchange should be considered in patients with severe acute kidney injury, as reported by Kidney International 4
• Plasma exchange may also be considered in patients with diffuse alveolar hemorrhage with hypoxemia, according to Kidney International 1, 3
• Azathioprine maintenance therapy should be started at 1.5-2 mg/kg/day for 18-24 months, then decreased to 1 mg/kg/day until 4 years after diagnosis, as described in Kidney International 5, 6
• Glucocorticoids should be continued at 5-7.5 mg/day for 2 years and then slowly reduced by 1 mg every 2 months, according to Kidney International 5, 6

Management of Relapse and Refractory Disease

• Patients with relapsing disease should be reinduced, preferably with rituximab, as reported by Kidney International 1, 3
• Refractory disease can be treated by increasing glucocorticoids, adding rituximab, or considering plasma exchange, according to Kidney International 1, 3, 5

Treatment of ANCA-Associated Vasculitis with Renal Involvement

Immediate Management

• The American College of Rheumatology recommends immediate initiation of remission induction therapy with rituximab or cyclophosphamide plus high-dose glucocorticoids in patients with severe, organ-threatening disease, without waiting for biopsy confirmation 7, 8
• Do not delay immunosuppressive therapy while awaiting kidney biopsy when clinical presentation strongly suggests AAV with positive ANCA serology, especially in rapidly deteriorating patients 8
• The combination of upper respiratory tract involvement, lower respiratory tract disease, palpable purpura, constitutional symptoms, positive ANCA, and glomerulonephritis with RBC casts is diagnostic for severe GPA 7, 8
• About 90% of patients with small-vessel vasculitis have ANCA directed against MPO or PR3, and a positive test with compatible clinical features is sufficient to begin treatment 8

Remission Induction Regimen

• Rituximab is conditionally recommended for remission induction in severe GPA/MPA by the American College of Rheumatology 7, 9
• Cyclophosphamide can be used as an alternative to rituximab, with a dose of 2 mg/kg/day for 3-6 months 7
• High-dose glucocorticoids, such as methylprednisolone 500-1000 mg IV daily for 3 days, followed by prednisone 1 mg/kg/day, should be used in combination with rituximab or cyclophosphamide 7, 8

Maintenance Therapy

• The American College of Rheumatology recommends beginning maintenance therapy after achieving remission, typically by 4-6 months, with rituximab at fixed intervals or azathioprine 7, 9
• Rituximab dosing for maintenance therapy is 500 mg IV every 6 months for at least 18-24 months 7

Treatment Setting

• Patients with AAV should be treated at centers with experience in AAV management, given the complexity of induction therapy, monitoring for treatment toxicity, and long-term relapse prevention 8

Urgent Management Strategies for Suspected ANCA‑Associated Vasculitis

Remission‑Induction Therapy

• High‑dose glucocorticoid taper – After an initial course of intravenous methylprednisolone (500–1000 mg daily for 3 days) followed by oral prednisone (≈1 mg/kg/day, max 80 mg), a predefined tapering schedule should be started to minimize steroid‑related toxicity. 10
• Rituximab regimen (preferred) – Administer rituximab 375 mg/m² intravenously once weekly for four consecutive weeks as part of remission induction. 10
• Cyclophosphamide regimen (alternative) – Use oral cyclophosphamide 2 mg/kg/day for a duration of 3–6 months when rituximab is not suitable. 10

Adjunctive Plasma‑Exchange

• Severe acute kidney injury – Consider plasma exchange in patients presenting with rapidly progressive renal failure (e.g., sharply falling glomerular filtration rate) to improve renal outcomes. 10
• Diffuse alveolar hemorrhage – Initiate plasma exchange for patients with widespread alveolar bleeding accompanied by hypoxemia to reduce respiratory mortality. 10

Tissue‑Biopsy Strategy

• Skin biopsy – Obtain a prompt skin biopsy of an active lesion to confirm necrotizing small‑vessel vasculitis; however, do not postpone immunosuppressive therapy while awaiting pathology results. [10][11]
• Kidney biopsy diagnostic yield – In cases with renal involvement, kidney biopsy provides a diagnostic yield of approximately 91 % for granulomatosis with polyangiitis and offers important prognostic information. [10][11]
• Bleeding risk after renal biopsy – Be aware that the risk of post‑biopsy bleeding is increased in patients who have received plasma exchange, so timing of the procedure should be carefully planned. 10

Referral to Specialized Centers

• Transfer to expert centers – Patients with suspected organ‑threatening ANCA‑associated vasculitis should be transferred to facilities with dedicated vasculitis programs that can deliver rapid ANCA testing, expert histopathology interpretation, access to rituximab and plasma‑exchange protocols, intensive‑care and dialysis capabilities, and coordinated long‑term follow‑up. [10][11]

Association of p‑ANCA/MPO with Microscopic Polyangiitis and ANCA‑Associated Vasculitis Classification

Antibody Specificity and Disease Association

• p‑ANCA/MPO antibodies are most strongly linked to microscopic polyangiitis (MPA), a small‑vessel vasculitis that lacks granulomatous inflammation. 12

Classification of ANCA‑Associated Vasculitides

• The spectrum of ANCA‑associated vasculitides (AAV) includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). 12
• A focal necrotizing glomerular pattern together with p‑ANCA/MPO positivity most commonly signifies MPA or kidney‑limited vasculitis, whereas GPA is typically associated with c‑ANCA/PR3 antibodies. 12

Renal Pathology in ANCA‑Associated Vasculitis: Distinguishing Primary FSGS from Secondary Focal Global Glomerulosclerosis

Pathologic Hallmarks of ANCA‑Associated Vasculitis

• In patients with ANCA‑associated vasculitis, the characteristic renal lesion is pauci‑immune necrotizing and crescentic glomerulonephritis, not primary focal segmental glomerulosclerosis (FSGS). [Evidence: expert review, 2024] 13

Frequency and Nature of Focal Global Glomerulosclerosis

• Focal global glomerulosclerosis appears as a chronic, secondary feature in ANCA‑associated glomerulonephritis, involving roughly 10 %– 40 % of glomeruli and reflecting prior inflammatory injury. [Evidence: consensus of the American Society of Nephrology, 2016] [14][15]16
• This entity is fundamentally different from primary FSGS, which shows segmental sclerosis within individual glomeruli together with podocyte foot‑process effacement. [Evidence: expert consensus, 2016] 14

Biopsy Interpretation in Clinical Practice

• When a kidney biopsy is performed in a patient with MPO‑ANCA or PR3‑ANCA positivity, the primary diagnosis is ANCA‑associated glomerulonephritis, and the dominant pattern of injury is necrotizing and crescentic GN. [Evidence: expert review, 2024; consensus, 2016] [14][15]13
• Additional histologic findings may include focal global glomerulosclerosis, representing chronic scarring from earlier episodes of inflammation. [Evidence: consensus, 2016] [14][15]16
• The histopathologic classification system for ANCA‑associated GN emphasizes the proportion of normal glomeruli, crescentic glomeruli, and globally sclerotic glomeruli to guide prognosis. [Evidence: expert review, 2024] 13

Exceptions and Pitfalls

• A solitary low‑quality case report from 1996 described ANCA positivity in a patient whose biopsy showed FSGS; however, this anecdotal observation does not establish a causal link between ANCA vasculitis and primary FSGS. [Evidence: expert consensus, 2016] [14][15]16
• Clinicians must avoid conflating “focal global glomerulosclerosis” (entirely scarred glomeruli, a chronic sequela of many renal diseases including ANCA vasculitis) with “focal segmental glomerulosclerosis” (segmental podocyte‑driven injury). [Evidence: consensus, 2016] [14][15]16