Systemic Vasculitis Classification
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Direct answer
Systemic vasculitis is classified by the size of the vessel involved, into large, medium, small and variable vessel groups, using the nomenclature of the Chapel Hill Consensus Conference. ANCA status is the key separator within the small vessel group, which contains granulomatosis with polyangiitis, microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. Matching the organ pattern with the vessel size is the most reliable way to name the disease in an exam.
What you must remember
- Large vessel: Giant cell arteritis, usually after age 50 with headache, jaw claudication and visual loss, and Takayasu arteritis, in young women with pulse deficits.
- Medium vessel: Polyarteritis nodosa, which spares the glomeruli and is often linked to hepatitis B, and Kawasaki disease, with coronary aneurysms in children.
- PR3 ANCA: Granulomatosis with polyangiitis, causing sinus disease, saddle nose, lung nodules and necrotising glomerulonephritis.
- MPO ANCA: Microscopic polyangiitis, with glomerulonephritis and no granulomas, and eosinophilic granulomatosis with polyangiitis, with asthma and eosinophilia.
- Non-ANCA small vessel: IgA vasculitis with palpable purpura, arthritis and abdominal pain in children, and cryoglobulinaemic vasculitis, often linked to hepatitis C.
- Variable vessel: Behcet disease, with recurrent oral and genital ulcers, uveitis and a positive pathergy test in some regions.
A worked pathway for a man with sinusitis and a rising creatinine
A 58-year-old man has three months of sinus congestion, a saddle deformity of the nose and haematuria. His creatinine has risen over two weeks, urine shows red cell casts, and PR3 ANCA is positive.
- Place the vessel size: Upper airway disease, lung nodules and glomerulonephritis place him in the small vessel ANCA-associated group, pointing to granulomatosis with polyangiitis rather than a medium vessel disease.
- Confirm the lesion: Renal biopsy confirms pauci-immune crescentic glomerulonephritis, and chest imaging is checked for nodules or cavitation.
- Start induction: Severe kidney failure is treated with induction immunosuppression, typically cyclophosphamide or rituximab with corticosteroids.
- Consider plasma exchange: It is sometimes considered when creatinine is severely raised, although the PEXIVAS trial found no clear overall benefit.
Now take a 40-year-old woman with long-standing asthma, eosinophilia and multiple mononeuritis, with MPO ANCA positivity. The asthma and eosinophilia point to eosinophilic granulomatosis with polyangiitis, which is distinguished from GPA by its tissue eosinophilia and corticosteroid responsiveness.
Where the exam tries to catch you
Vasculitis vignettes are usually decided by the antibody target and the organ pattern.
- Trap: Equating ANCA positivity with granulomatosis with polyangiitis. Correct: PR3 ANCA is typical of GPA, while MPO ANCA is more typical of microscopic polyangiitis and EGPA, so the target is read with the clinical picture.
- Trap: Choosing polyarteritis nodosa when ANCA-positive kidney disease is present. Correct: Polyarteritis nodosa is a medium vessel disease that spares the glomerulus, so renal impairment with ANCA positivity points to a small vessel disease.
- Trap: Mixing up Kawasaki disease and IgA vasculitis. Correct: Kawasaki disease is tested by fever for five days with mucocutaneous changes, and IgA vasculitis by palpable purpura on the legs with nephritis.
- Trap: Delaying treatment while waiting for a temporal artery biopsy. Correct: Steroids given before biopsy reduce its yield, so treatment in suspected giant cell arteritis should not wait for the biopsy.
Frequently asked questions
Which ANCA target is typical of granulomatosis with polyangiitis?
Proteinase 3 ANCA, seen as cytoplasmic staining on immunofluorescence, is typical of granulomatosis with polyangiitis. MPO ANCA is more typical of microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis, which is why the antibody target is interpreted with the clinical picture.
Which vasculitis is linked to asthma and eosinophilia?
Eosinophilic granulomatosis with polyangiitis is the small vessel vasculitis linked to asthma, eosinophilia and sinus disease. Its ANCA status is variable, and it is distinguished from granulomatosis with polyangiitis by the asthma history and tissue eosinophilia.
Which medium vessel vasculitis typically spares the glomeruli?
Polyarteritis nodosa affects medium-sized arteries and typically spares the glomeruli, causing mononeuritis multiplex, hypertension and visceral infarcts. Renal angiography may show microaneurysms, and the condition is commonly associated with hepatitis B infection.
Why is giant cell arteritis classified as a large vessel vasculitis?
Giant cell arteritis involves the aorta and its major branches, especially cranial arteries such as the temporal artery, so it is grouped among large vessel vasculitides. It occurs mainly after age 50 and presents with headache, jaw claudication and a risk of sudden visual loss.