Vasculitis: classification and mechanisms
- Topic
Vasculitis is inflammation of the vessel wall. The size of the vessels involved and the immune mechanism decide the disease.
What it is
Vasculitis means inflammation of the vessel wall. It can come from direct infection of the wall or, more often, from immune mechanisms: immune complexes deposited in the wall, antineutrophil cytoplasmic antibodies (ANCA) that activate neutrophils, antibodies against endothelial cells, or T-cell mediated granulomatous inflammation. The consensus classification groups the non-infectious vasculitides by the calibre of vessel they mainly attack: large, medium or small; small-vessel disease is split into ANCA-associated and immune-complex types.
Step by step
- A trigger (infection, drug, tumour antigen or unknown) starts an immune response.
- Immune complexes deposit in the wall, or ANCA bind primed neutrophils, or T cells react against wall antigens.
- Complement and Fc receptors call in neutrophils; their enzymes and oxidants destroy the wall (fibrinoid necrosis).
- The damaged vessel thromboses, bleeds or forms aneurysms; the tissue downstream becomes ischemic.
- Healing leaves fibrosis and narrowing of the vessel.
Non-infectious vasculitis at a glance
| Disease | Vessel size | Key pathology | Key clue |
|---|---|---|---|
| Giant cell arteritis | Large (and medium) arteries of the head and aorta | Granulomatous arteritis with giant cells, fragmented elastic lamina | Over 50, headache, jaw claudication, high ESR, blindness risk |
| Takayasu arteritis | Aorta and its main branches | Granulomatous arteritis, then fibrosis | Young women, weak arm pulses (‘pulseless disease’) |
| Polyarteritis nodosa | Medium (and small) muscular arteries | Segmental fibrinoid necrosis, lesions of different ages, aneurysms | Kidney, gut, nerve, skin; spares lungs; hepatitis B in some |
| Kawasaki disease | Large to medium, especially coronary arteries | Transmural arteritis, coronary aneurysms | Child under 5, fever, mucocutaneous signs |
| Thromboangiitis obliterans | Medium and small arteries and veins of limbs | Inflammatory thrombus with microabscesses | Young heavy smokers, digital gangrene |
| Granulomatosis with polyangiitis | Small to medium | Necrotizing granulomas plus vasculitis | Upper and lower airways and kidney; PR3-ANCA |
| Microscopic polyangiitis | Small | Fibrinoid necrosis, lesions of one age, no granulomas | Lung capillaritis and glomerulonephritis; MPO-ANCA |
| Eosinophilic granulomatosis with polyangiitis | Small to medium | Eosinophil-rich necrotizing granulomas and vasculitis | Asthma, eosinophilia; MPO-ANCA in about half |
| IgA vasculitis | Small | Leukocytoclastic vasculitis with IgA deposits | Child, palpable purpura of buttocks and legs, arthralgia, abdominal pain, nephritis |
| Cryoglobulinemic vasculitis | Small | Cryoglobulin deposits, leukocytoclastic vasculitis | Hepatitis C, purpura, low complement |
Clinical notes
- Common signs: fever, weight loss, palpable purpura, mononeuritis multiplex, glomerulonephritis, lung hemorrhage, ischemic pain.
- ANCA testing, complement levels and hepatitis serology help sort the small-vessel forms.
Test yourself
Think of the answer, then tap the question to see it.
Which vasculitides are associated with PR3-ANCA and with MPO-ANCA?
PR3-ANCA: granulomatosis with polyangiitis. MPO-ANCA: microscopic polyangiitis and, in about half, eosinophilic GPA.
Why are ANCA-associated vasculitides called pauci-immune?
Because the vessel lesions show little or no immunoglobulin and complement by immunofluorescence, unlike immune-complex vasculitis.
What two large-vessel vasculitides are separated mainly by age?
Giant cell arteritis (over 50) and Takayasu arteritis (usually under 50, mostly young women).
Elsewhere in DurgiPedia
- Type III hypersensitivity (immune complexes)
- Autoantibodies: the table to know
- Hypersensitivity: the four types compared
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Vasculitis| Angiitis | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.