Microscopic polyangiitis
Microscopic polyangiitis (MPA) is a pauci-immune small-vessel vasculitis, almost always with perinuclear antineutrophil cytoplasmic antibody (p-ANCA) targeting myeloperoxidase (MPO), that causes rapidly progressive crescentic glomerulonephritis and pulmonary alveolar hemorrhage without the granulomas, eosinophilia, or upper-airway disease of its ANCA-associated siblings. Diagnosis combines urine microscopy, ANCA serology, and biopsy, and treatment is glucocorticoids plus rituximab or cyclophosphamide induction followed by rituximab or azathioprine maintenance.
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What this article covers
- Overview
Definition: microscopic polyangiitis (MPA) is a pauci-immune necrotizing vasculitis of small vessels, capillaries, venules, and arterioles, that is antineutrophil cytoplasmic antibody (ANCA)…
- Epidemiology
Rarer than GPA: annual incidence is about 2.7 per million in Europe, lower elsewhere, versus 7 to 12 per million for GPA.
- Risk factors
Age: most patients present between 50 and 70 years old.
- Pathophysiology
ANCA specificity: p-ANCA against myeloperoxidase (MPO-ANCA) predominates (50 to 75% of patients), in contrast to the c-ANCA/anti-proteinase 3 (PR3) pattern that predominates in GPA; a minority of MPA…
- Clinical features
Constitutional prodrome: fever, malaise, weight loss, arthralgia, and myalgia commonly precede organ-specific disease.
- Differential diagnosis
Granulomatosis with polyangiitis: shares pulmonary hemorrhage and pauci-immune crescentic glomerulonephritis, but affects the upper airway (sinusitis, nasal crusting, saddle-nose deformity), shows…
- Diagnosis
What establishes the diagnosis: a compatible clinical picture, renal and/or pulmonary involvement with a pauci-immune pattern, together with p-ANCA/anti-MPO positivity, makes the diagnosis highly likely; ANCA negativity does not exclude MPA.
- Management
First, for organ-threatening or life-threatening disease, pulse then taper glucocorticoids: Methylprednisolone 500 to 1000 mg IV once daily for 3 days.
- Complications
End-stage kidney disease: the consequence of unchecked pauci-immune crescentic glomerulonephritis, in up to 25% of survivors within 4 years.
- Prognosis
Renal involvement drives early mortality: ANCA-associated glomerulonephritis, the dominant feature of MPA, carries about 20% mortality within the first year, and up to 25% of survivors progress to end-stage kidney disease within 4 years.
- Prevention
No primary prevention exists: MPA is idiopathic in most cases; when drug induced, stopping the offending agent is the only preventive measure.
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Related articles
- Granulomatosis with polyangiitis
Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated necrotizing granulomatous vasculitis of the upper airway, lower airway, and kidney, most often with cytoplasmic ANCA (c-ANCA) targeting proteinase 3 (PR3). Diagnosis rests on the clinical triad, ANCA serology, and tissue biopsy showing pauci-immune vasculitis, and treatment begins with high-dose glucocorticoids plus rituximab or cyclophosphamide for organ-threatening disease, followed by rituximab or azathioprine maintenance.
- Eosinophilic granulomatosis with polyangiitis
Eosinophilic granulomatosis with polyangiitis (EGPA) is the rarest antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, defined by a three-phase course of late-onset asthma and rhinosinusitis, then peripheral and tissue eosinophilia, then small- and medium-vessel vasculitis with mononeuritis multiplex. ANCA is positive in only 40 to 60 percent of patients, cardiac involvement drives most mortality, and treatment is glucocorticoids alone for non-organ-threatening disease, glucocorticoids plus cyclophosphamide or rituximab for organ-threatening disease, and mepolizumab as steroid-sparing therapy.
- Polyarteritis nodosa
Polyarteritis nodosa is a rare, antineutrophil cytoplasmic antibody (ANCA)-negative necrotizing vasculitis of medium and small arteries that spares the lungs and spares glomeruli, presenting with constitutional illness, mononeuritis multiplex, livedo reticularis, mesenteric ischemia, and renovascular hypertension. Diagnosis rests on biopsy or mesenteric/renal angiography, and treatment is glucocorticoids plus cyclophosphamide for severe idiopathic disease, or a short glucocorticoid course with antiviral therapy and plasma exchange when hepatitis B-associated.
- Anti-glomerular basement membrane (anti-GBM) disease
Anti-glomerular basement membrane (anti-GBM) disease is a rare, rapidly progressive glomerulonephritis caused by circulating antibodies against the alpha-3 chain of type IV collagen, presenting with hematuria, acute kidney injury, and, in over half of patients, pulmonary hemorrhage (Goodpasture syndrome). Kidney biopsy showing crescentic glomerulonephritis with linear IgG staining plus a positive serum anti-GBM antibody confirms the diagnosis, and outcome depends critically on early treatment with plasma exchange, pulse glucocorticoids, and cyclophosphamide before dialysis dependence and diffuse crescents set in.
- Rapidly progressive glomerulonephritis
Rapidly progressive glomerulonephritis is a clinical syndrome defined by at least a 50% decline in glomerular filtration rate over days to weeks with extensive glomerular crescents on biopsy, most often from ANCA-associated, anti-glomerular basement membrane, or immune-complex glomerulonephritis. Untreated disease progresses to dialysis within days to weeks, so kidney biopsy and etiology-directed immunosuppression must begin urgently.
- Vasculitis: an overview
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