Microscopic polyangiitis !

An autoimmune inflammation of small blood vessels that mainly damages the kidneys and lungs, often with MPO-ANCA antibodies and no granulomas.

Updated 2026-11-01

Structures involved

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Why it happens

What it is

A necrotising small-vessel vasculitis with few or no immune deposits (pauci-immune) and no granulomas. It is one of the ANCA-associated vasculitides, typically with MPO-ANCA (p-ANCA). Its main targets are the kidneys (rapidly progressive glomerulonephritis) and the lungs (alveolar haemorrhage or fibrosis), forming a pulmonary-renal syndrome.

Who gets it

An uncommon disease that usually starts after 50 years and affects both sexes. It is more frequent than granulomatosis with polyangiitis in Asia and southern Europe, and in Latin American series MPO-ANCA vasculitis is relatively common among ANCA-associated vasculitides.

Causes

Autoimmune loss of tolerance to myeloperoxidase (MPO) in neutrophils
Genetic susceptibility (HLA-DQ alleles)
Environmental triggers such as silica exposure and infections
Some drugs (hydralazine, propylthiouracil, levamisole-adulterated cocaine) can induce MPO-ANCA vasculitis

Risk factors

Age over 50 years
Occupational silica exposure
Exposure to inducing drugs, including cocaine adulterated with levamisole
Pre-existing interstitial lung disease in some patients

Pathophysiology

ANCA bind to MPO expressed on cytokine-primed neutrophils, which then degranulate and release reactive oxygen species and NETs against endothelium, causing fibrinoid necrosis of arterioles, capillaries and venules. In the glomerulus this produces focal necrotising crescentic glomerulonephritis; in the lung, capillaritis with alveolar haemorrhage. Unlike granulomatosis with polyangiitis, there are no granulomas and the upper airway is usually spared.

Symptoms and signs

Fever, weight loss, fatigue and joint or muscle pain
Dark urine, oedema and high blood pressure from glomerulonephritis
Cough, breathlessness and haemoptysis
Palpable purpura on the legs
Numbness, pain or foot drop from mononeuritis multiplex

Diagnosis

Clinical: Consider in any patient with a pulmonary-renal syndrome, rapidly progressive kidney failure with active urine sediment, or systemic illness with purpura and mononeuritis multiplex. Classification uses the 2022 ACR/EULAR criteria.
Tests: MPO-ANCA (p-ANCA) by ELISA in most patients; creatinine, electrolytes, urinalysis with microscopy (dysmorphic red cells, red cell casts) and urine protein; blood count, ESR and CRP; anti-GBM antibodies and complement to exclude other causes. Kidney biopsy shows pauci-immune necrotising crescentic glomerulonephritis and confirms the diagnosis.
Imaging: Chest CT for alveolar haemorrhage (ground-glass opacities) or interstitial fibrosis; bronchoscopy with lavage can confirm bleeding and exclude infection.

Differential diagnosis

Granulomatosis with polyangiitis
Anti-GBM disease (Goodpasture)
Lupus nephritis
Eosinophilic granulomatosis with polyangiitis
Polyarteritis nodosa (medium vessels, no glomerulonephritis, ANCA negative)
Infective endocarditis and post-infectious glomerulonephritis

Goal of treatment

Induce remission rapidly to save kidney and lung function, then maintain remission while limiting infection and drug toxicity.

Treatment

Acute: Diffuse alveolar haemorrhage or rapidly progressive glomerulonephritis is an emergency: hospital admission, oxygen or ventilation, dialysis if needed and immediate immunosuppression.
Medical: Induction with high-dose systemic corticosteroids (with planned rapid tapering) plus rituximab or cyclophosphamide; avacopan may help reduce steroid exposure.
Procedure: Plasma exchange may be considered in selected patients with severe kidney failure or alveolar haemorrhage.
Medical: Maintenance with rituximab or azathioprine for at least two years; prophylaxis against Pneumocystis and bone protection during steroid therapy.
Follow-up: Monitoring of creatinine, urine sediment, blood counts, ANCA trend and infection; nursing care includes fluid balance, blood pressure, and watching for bleeding and haemoptysis.

Complications

End-stage kidney disease requiring dialysis or transplant
Diffuse alveolar haemorrhage and respiratory failure
Pulmonary fibrosis
Serious infections from immunosuppression
Relapse of vasculitis

Prognosis

Untreated it is usually fatal; with modern induction most patients achieve remission and five-year survival is around 75–80%. Kidney function at diagnosis predicts outcome, and relapses occur, though less often than in PR3-ANCA disease.

Test yourself

Think of the answer, then tap the question to see it.

Which ANCA is typical of microscopic polyangiitis?

MPO-ANCA (p-ANCA).

What histological feature distinguishes microscopic polyangiitis from granulomatosis with polyangiitis?

The absence of granulomas (and usually of upper airway involvement).

What does kidney biopsy show?

Pauci-immune focal necrotising crescentic glomerulonephritis.

Which two organs together form the classic pulmonary-renal syndrome in this disease?

The lungs (alveolar haemorrhage) and kidneys (rapidly progressive glomerulonephritis).

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Microscopic Polyangiitis (Johns Hopkins Vasculitis Center, 2026); Vasculitis (MedlinePlus (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.

Kidneys highlighted on the Durgical 3D model