Microscopic Polyangiitis

Microscopic Polyangiitis

Surya V. Seshan, MD

MPO-ANCA-mediated crescentic glomerulonephritis shows segmental transmural necrotizing small vessel vasculitis image adjacent to a glomerulus with circumferential crescent image.

Two glomeruli show segmental pauci-immune type glomerulonephritis with small cellular crescents image in the Bowman space. The remaining portions of the glomeruli are unremarkable.



  • Microscopic polyangiitis (MPA)


  • Microscopic polyarteritis

  • p-ANCA mediated small vessel vasculitis

  • Systemic or renal limited crescentic glomerulonephritis

  • “Pauci-immune” glomerulonephritis


  • Chapel Hill Consensus Conference

    • Necrotizing vasculitis, with few or no immune deposits, affecting small vessels (i.e., capillaries, venules, or arterioles)

    • Necrotizing arteritis involving small and medium-sized arteries may be present

    • Necrotizing glomerulonephritis is very common

    • Pulmonary capillaritis often occurs


Environmental Exposure

  • Higher rate of onset in winter than summer

    • Similar to granulomatosis with polyangiitis (Wegener)


  • Anti-neutrophil cytoplasmic antibody (ANCA)-mediated small vessel vasculitis

    • Mainly autoantibodies to antigen myeloperoxidase (p-ANCA)

    • Minority have autoantibodies to antigen proteinase 3 (c-ANCA)

    • Subset of MPO-ANCA small vessel vasculitis is renal-limited necrotizing crescentic glomerulonephritis

    • Subset are ANCA(-) renal-limited necrotizing crescentic glomerulonephritis

  • Cell-mediated immune mechanism with T-lymphocytes, neutrophils, and histiocytes are necessary for development of crescentic glomerulonephritis

    • ANCA-activated neutrophils tend to adhere to activated microvascular endothelium to initiate injury

    • Alternate pathway of complement has been shown to initiate and enhance endothelial injury and vasculitis



  • Incidence

    • Varies with geographic locations

      • 1-8/1,000,000 in Europe and United States

      • 10-24/1,000,000 in Asian and Arab countries

  • Age

    • All ages affected

    • Average age at onset is 50 years

  • Ethnicity

    • Geographic variations may be related to ethnic background


  • General

    • Pulmonary renal syndrome

    • Constitutional symptoms (up to 75%)

      • Fever, weakness, weight loss

      • Arthralgias, myalgias (25-50%)

      • Hypertension

  • Renal (90-100%)

    • Kidney is common organ involved in MPA

    • Hematuria

    • Proteinuria

    • Renal insufficiency

    • Rapidly progressive or oliguric acute renal failure

  • Skin

    • Purpuric rash, palpable (45%)

  • Lung (25-55%)

    • Hemoptysis

    • Dyspnea

    • Pulmonary hemorrhage

    • Lung infiltrates

  • Gastrointestinal (50%)

    • Abdominal pain

      • Severe form with bowel perforation

    • Hepatomegaly

  • Neurologic (30%)

    • Peripheral neuropathy less frequent than PAN

    • Central nervous system

  • Ear, nose, throat (30-35%)

    • Mouth ulcers

    • Epistaxis

    • Sinusitis

Laboratory Tests

  • Anemia (normochromic normocytic)

  • Elevation of acute phase proteins

    • Erythrocyte sedimentation rate

    • C-reactive protein

  • Leukocytosis and thrombocytosis

  • Rheumatoid factor (39-50%)

  • Antinuclear antibodies (21-33%)

  • p-ANCA/anti-myeloperoxidase positive (60%)

  • c-ANCA/anti-PR3 positive (15%)

  • Renal

    • Urinalysis shows red cells and RBC casts

    • Varying degrees of proteinuria

    • Elevated serum BUN and creatinine levels


  • Remission induction, remission maintenance, and relapse treatment are 3 phases of therapy

  • Corticosteroids combined with cyclophosphamide is most common induction protocol

  • Other forms of immunosuppressive therapy in refractory cases (10%)

  • Oral cyclophosphamide, mycophenolate mofetil, or azathioprine used for remission maintenance


  • Severe form of glomerular disease with aggressive course

  • 1-year mortality rate of untreated cases is 80%

  • Early deaths are usually due to fulminant renal disease and lung hemorrhage in MPA

  • Frequent relapses occur (25-35%)

    • Different or new organs may be involved during relapses

    • Often associated with rash and arthralgias

    • Generally less severe

  • Induction protocol

    • Improvement in > 90% of patients

    • Complete remission in > 75%

  • Independent factors that correlate with worse prognosis are older age, higher initial serum creatinine, and pulmonary hemorrhage

  • Pathologic parameters representative of recovery of renal function include percent of normal glomeruli at initial biopsy, tubular injury, glomerular crescents, and interstitial inflammation


General Features

  • Normal or mildly increased kidney size

  • Infarcts when present are small

  • Petechial hemorrhages

    • Focal or diffuse

    • Represent glomerular necrosis; hemorrhage in Bowman space or within tubular lumina


Histologic Features

Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Microscopic Polyangiitis
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