[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › Microscopic polyangiitis

[Conditions](https://durgical.com/en/conditions/) · [Rheumatology](https://durgical.com/en/conditions/)

# 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

Tap one to see what it is and open it in 3D.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Vessels inside the kidney](https://durgical.com/en/anatomy/intrarenal-arteries-and-veins/)
- [Ureters](https://durgical.com/en/anatomy/ureter/)
- [Segmental lung vessels](https://durgical.com/en/anatomy/pulmonary-trunk-chest/)
- [Pleura](https://durgical.com/en/anatomy/pleura/)
- [Skin](https://durgical.com/en/anatomy/skin/)
- [Common fibular nerve](https://durgical.com/en/anatomy/common-fibular-nerve/)
- [Sural nerves](https://durgical.com/en/anatomy/sural-nerve/)

## Why it happens

- [When leukocytes injure tissue: proteases, oxidants and NETs](https://durgical.com/en/general-pathology/when-leukocytes-injure-tissue-proteases-oxidants-and-nets/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)
- [Blood vessels: artery, vein and capillary layers](https://durgical.com/en/histology/blood-vessels-artery-vein-and-capillary-layers/)
- [Glomerulus and the filtration barrier: podocytes, mesangium, JGA](https://durgical.com/en/histology/glomerulus-and-the-filtration-barrier-podocytes-mesangium-jga/)
- [The alveolus: type I and II pneumocytes, surfactant, the blood–air barrier](https://durgical.com/en/histology/the-alveolus-type-i-and-ii-pneumocytes-surfactant-the-blood-air-barrier/)

## 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

## Red flags

- Haemoptysis with falling haemoglobin and hypoxaemia (diffuse alveolar haemorrhage)
- Rapid rise in creatinine, oliguria or hyperkalaemia
- Haematuria with red cell casts and proteinuria in an older adult with systemic symptoms
- Mesenteric ischaemia or new neurological deficit

## Diagnosis

**Clinical**
Consider in any patient with a pulmonary-renal syndrome, rapidly progressive [kidney](https://durgical.com/en/anatomy/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](https://durgical.com/en/anatomy/region/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).

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/microscopic-polyangiitis/)

## Related conditions

- [Granulomatosis with polyangiitis](https://durgical.com/en/conditions/granulomatosis-with-polyangiitis/)
- [Eosinophilic granulomatosis with polyangiitis (Churg–Strauss)](https://durgical.com/en/conditions/eosinophilic-granulomatosis-with-polyangiitis/)
- [Polyarteritis nodosa](https://durgical.com/en/conditions/polyarteritis-nodosa/)
- [Rapidly progressive glomerulonephritis (anti-GBM, ANCA)](https://durgical.com/en/conditions/rapidly-progressive-glomerulonephritis/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Lupus nephritis](https://durgical.com/en/conditions/lupus-nephritis/)
- [Peripheral neuropathy (diabetic and other)](https://durgical.com/en/conditions/peripheral-neuropathy/)
- [IgA vasculitis (Henoch–Schönlein purpura)](https://durgical.com/en/conditions/iga-vasculitis/)

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

Sources: [Microscopic Polyangiitis](https://www.hopkinsvasculitis.org/types-vasculitis/microscopic-polyangiitis/) (Johns Hopkins Vasculitis Center, 2026); [Vasculitis](https://medlineplus.gov/vasculitis.html) (MedlinePlus (U.S. National Library of Medicine), 2026).

[← All conditions](https://durgical.com/en/conditions/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/conditions/microscopic-polyangiitis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/microscopic-polyangiitis/