What are the differential diagnoses for intimal arteritis on a renal biopsy?

Differential Diagnosis of Intimal Arteritis on Renal Biopsy

Intimal arteritis on renal biopsy requires consideration of ANCA-associated vasculitis (particularly microscopic polyangiitis and granulomatosis with polyangiitis), anti-GBM disease, systemic lupus erythematosus with lupus vasculopathy, drug-induced vasculitis, and in transplant patients, acute rejection—with the clinical context, serologic testing, and timing being critical to distinguish between these entities.

Primary Vasculitic Causes

ANCA-Associated Vasculitis (AAV)

• MPO-ANCA or PR3-ANCA positive small-vessel vasculitis is the most common cause of intimal arteritis in native kidneys, with approximately 90% of patients with necrotizing crescentic glomerulonephritis having positive ANCA serology 1.
• The kidney biopsy in AAV typically shows necrotizing arteritis with fibrinoid necrosis, crescentic glomerulonephritis, and pauci-immune features (negative immunofluorescence) 1.
• Importantly, 10% of patients with clinical AAV are persistently ANCA-negative, yet are treated identically to ANCA-positive patients 1.
• Even with minimal urinary abnormalities and normal renal function, kidney biopsy may reveal small-vessel arteritis and necrotizing glomerulonephritis in MPO-ANCA positive patients 2.

Anti-GBM Disease

• Anti-GBM antibody disease (formerly Goodpasture syndrome) presents with necrotizing and crescentic glomerulonephritis, often severe, and can involve arteritis 3.
• This diagnosis is critical to identify urgently as it requires immediate plasma exchange without waiting for biopsy confirmation when serologic testing is positive 1.
• Some patients have dual positivity for both ANCA and anti-GBM antibodies, representing an overlap syndrome 1.

Lupus Vasculopathy

• Systemic lupus erythematosus can cause lupus vasculopathy characterized by concentric intimal thickening with narrowed arterial lumens 4.
• The biopsy shows deposition of IgG/IgM/complement 3 in arteriolar walls, which distinguishes it from pauci-immune AAV 4.
• This can occur without active glomerular lesions or immune complex deposition in glomeruli, yet still cause renal infarction and dysfunction 4.
• Thrombotic microangiopathy associated with antiphospholipid antibodies in lupus should be considered part of the primary disease when present 3.

Secondary and Non-Vasculitic Causes

Drug-Induced Vasculitis

• Medications, particularly trimethoprim-sulfamethoxazole, can cause acute interstitial nephritis with intimal arteritis that mimics acute rejection or primary vasculitis 5.
• Key diagnostic feature: improvement of renal function after drug discontinuation without immunosuppressive therapy 5.
• The biopsy may show severe interstitial infiltration with eosinophils, severe tubulitis, and intimal arteritis 5.

Transplant-Related Intimal Arteritis (v-lesions)

• In kidney transplant patients, intimal arteritis (v-lesions) has complex and variable significance that differs substantially from native kidney arteritis 6.
• Isolated v-lesions without tubulointerstitial inflammation (i-t) often do not represent true rejection, with 79% showing no molecular rejection in one study 6.
• Timing post-transplant is critical: early isolated v-lesions (<1 year) are usually DSA-negative with no molecular rejection, while late isolated v-lesions (>1 year) often have positive DSA and antibody-mediated rejection 6.
• When v-lesions occur with significant tubulointerstitial inflammation (i-t-v pattern), 95% show molecular T-cell mediated rejection 6.
• The Banff classification distinguishes type 2A (focal arteritis) from type 2B (severe arteritis), with type 2B having worse initial response to therapy and a hazard ratio of 1.9 for graft failure 7.

Critical Diagnostic Approach

Serologic Testing Priority

• Obtain MPO-ANCA, PR3-ANCA, and anti-GBM antibodies immediately when intimal arteritis is suspected clinically 1.
• High-quality antigen-specific immunoassays are preferred over indirect immunofluorescence for ANCA testing 1.

Clinical Context Assessment

• Systemic features: fever, pulmonary hemorrhage (pulmonary-renal syndrome), skin lesions, or other organ involvement suggest primary vasculitis 1.
• Medication history: recent introduction of antibiotics or other drugs suggests drug-induced vasculitis 5.
• Transplant status and timing: if post-transplant, determine time from transplantation and DSA status 6.
• Lupus history: known SLE with hypertension and renal dysfunction suggests lupus vasculopathy 4.

Histologic Features to Assess

• Immunofluorescence pattern: pauci-immune (AAV), linear GBM staining (anti-GBM), or granular immune deposits (lupus) 1, 2, 4.
• Accompanying glomerular lesions: necrotizing crescentic GN strongly suggests AAV or anti-GBM disease 1.
• Tubulointerstitial inflammation: presence and severity, with eosinophils suggesting drug reaction 5.
• Vascular changes: concentric intimal thickening with immune deposits suggests lupus vasculopathy 4.

Common Pitfalls

• Do not delay treatment for biopsy confirmation when MPO/PR3-ANCA is positive with compatible clinical presentation, especially in rapidly deteriorating patients 1.
• Do not assume all intimal arteritis in transplants represents rejection—consider timing, DSA status, and presence of tubulointerstitial inflammation 6.
• Do not exclude AAV based on negative ANCA alone—10% of true AAV cases are ANCA-negative 1.
• Do not overlook drug-induced vasculitis—always review recent medication changes, particularly antibiotics 5.
• Consider secondary diagnoses such as atheroembolic disease, which should be listed separately per consensus guidelines 3.