What's microscopic polyangiitis?
Microscopic polyangiitis is an ANCA-associated small-vessel vasculitis: the immune system inflames and destroys the walls of small blood vessels, most often in the kidneys and lungs. It is pauci-immune (few immune deposits in the tissue) and non-granulomatous, which distinguishes it from the related ANCA vasculitides. Most people carry myeloperoxidase antibodies (MPO-ANCA).
| Also indexed as | ORPHA:727, MONDO:0019124 |
|---|---|
| Features mapped | 11 |
| Treatments mapped | 5 |
| Published sources | 13 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Multiple mononeuropathy
Microscopic polyangiitis can damage individual nerves in different parts of the body, a pattern doctors call mononeuritis multiplex, which may cause weakness or numbness in scattered areas.
Vasculitis
The underlying problem is a pauci-immune small-vessel vasculitis. 'Pauci-immune' means that, unlike some other kidney diseases, very few immune deposits are seen in the affected tissue under the microscope; the damage is driven by inflammatory cells rather than by trapped antibody complexes.
Anemia
Anemia (a low red-blood-cell count) is frequently found, reflecting the systemic inflammation and, when present, blood loss from the lungs or kidneys.
Diffuse alveolar hemorrhage
Microscopic polyangiitis can cause diffuse alveolar hemorrhage, which is bleeding into the small air sacs of the lungs.
Palpable purpura
Purpura is one of the most common skin signs of microscopic polyangiitis. It often appears as raised purple-red spots you can feel, usually on the lower legs, caused by inflammation of small blood vessels in the skin.
Hematuria
Blood in the urine that is only visible under a microscope (microscopic hematuria), often together with protein in the urine, is a common early signal of kidney involvement.
Anti-myeloperoxidase antibody positivity
Most people with microscopic polyangiitis carry an antibody called MPO-ANCA (anti-myeloperoxidase). A blood test showing this antibody is one of the findings that points toward the condition.
Glomerulonephritis
In microscopic polyangiitis, inflammation can damage the tiny filtering units of the kidneys, leading to a fast-worsening kidney problem doctors call rapidly progressive glomerulonephritis.
Renal insufficiency
Kidney function can decline rapidly. Because the decline can be fast and is a major driver of poor outcomes, early recognition and treatment matter a great deal.
Crescentic glomerulonephritis
A kidney biopsy in microscopic polyangiitis can show crescentic, pauci-immune glomerulonephritis, meaning the filtering units are inflamed and scarring into crescent shapes without the antibody deposits seen in some other kidney diseases.
Interstitial lung disease
Interstitial lung disease, inflammation and scarring of the lung tissue, can occur in microscopic polyangiitis and the related ANCA-associated vasculitides.
How it is diagnosed
Microscopic polyangiitis
Diagnosed using: MPO-ANCA testing.
“MPA was suspected based on rapidly progressive glomerulonephritis, mononeuritis multiplex, and myeloperoxidase (MPO)-ANCA…”
Microscopic polyangiitis
Diagnosed using: renal biopsy.
“The kidney biopsy demonstrated focal crescentic necrotizing glomerulonephritis pauci-immune type, confirming…”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
glucocorticoids
Glucocorticoids (steroids such as prednisolone, sometimes given first as intravenous methylprednisolone) are the backbone of initial treatment to bring the inflammation under control. Current practice leans toward reduced-dose regimens to limit steroid side effects.
Used to help with: Microscopic polyangiitis.
“…reduced-dose glucocorticoid (GC)…”
rituximab
Rituximab, an antibody that depletes the B cells that make the harmful autoantibodies, is now a central drug both for bringing the disease into remission and for keeping it there.
Used to help with: Microscopic polyangiitis.
“Rituximab is now central to remission induction and…”
cyclophosphamide
Cyclophosphamide, a potent immune-suppressing medicine, is the alternative induction agent, used especially in severe organ-threatening disease such as major lung or kidney involvement.
Used to help with: Microscopic polyangiitis.
“…followed by intravenous cyclophosphamide (500…”
avacopan
Avacopan is a newer oral drug that blocks the C5a receptor, part of the complement system that drives the inflammation. It was developed as a steroid-sparing option, helping reduce how much glucocorticoid a person needs.
Used to help with: Microscopic polyangiitis.
“Avacopan, a selective complement C5a receptor antagonist, has been introduced as a steroid-sparing…”
azathioprine
Azathioprine is one of the medicines used to treat microscopic polyangiitis. In one reported case, prednisolone combined with azathioprine led to rapid clearing of the skin purpura.
Used to help with: Microscopic polyangiitis.
“Based on these findings, MPA was diagnosed. Treatment with prednisolone and azathioprine resulted in the rapid resolution of the…”
What changes how it shows up
The diagnosis is not the whole story. The factors and open questions below are described in the research mapped here as shaping whether, or how strongly, the condition shows up, or as points the field has not yet settled. They are not, on their own, its cause or its cure.
relapsing course
Microscopic polyangiitis tends to follow a relapsing course: even after remission is reached, flare-ups during maintenance treatment are relatively common, which is why ongoing monitoring is part of care.
Described as modulating: Microscopic polyangiitis.
“Although relapse during maintenance therapy is relatively…”
How to read the evidence labels
Where this comes from
This guide is built from 13 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
Take it further
Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.