Vasculitis Classification — Chapel Hill 2012, Large, Medium and Small Vessel Vasculitis, ANCA Patterns

Vasculitis is inflammation of blood vessel walls that leads to end-organ damage. More than 30 distinct vasculitides are described. Primary systemic vasculitis is classified mainly by the International Chapel Hill Consensus Conference (CHCC 2012) nomenclature, which sorts diseases by the size of the vessel predominantly affected. In 2022, ACR/EULAR added new classification criteria for GPA, MPA, EGPA, GCA and Takayasu arteritis.

Both are granulomatous large-vessel vasculitides in which inflammation starts in the vasa vasorum of the adventitia and spreads through the wall. The main discriminator is age: GCA affects people over 50; Takayasu affects mostly women under 50.

Polyarteritis nodosa is a necrotising vasculitis of medium arteries with a well-established link to hepatitis B: immune complexes of viral antigen deposit in the vessel wall. Without hepatitis B it is extremely rare. It shows a slight male predominance and peaks at 40 to 60 years.

• Skin — palpable purpura, livedo reticularis, ulcers, digital ischaemia (mostly lower limbs).
• Kidney — renal artery vasculitis with infarction (non-glomerular disease); malignant hypertension is a key sign.
• Nerve — mononeuritis multiplex with wrist or foot drop.
• Gut and heart — mesenteric ischaemia, myocardial ischaemia; myalgia.
• Diagnosis — no specific blood test; hepatitis B and C serology; arteriography, CT or MR angiography shows stenoses and aneurysmal dilatations.

Kawasaki disease affects medium (and small) arteries in children, mainly under 5 years, with much higher rates in Japan, Korea and Taiwan. The danger is coronary artery aneurysm, so every suspected case needs ECG and echocardiography.

The three ANCA-associated vasculitides are pauci-immune small-vessel vasculitides: ANCAs prime neutrophils, which release proteinase-3 (PR3) and myeloperoxidase (MPO) and damage the endothelium. ANCA is found in 73–95% of GPA or MPA cases, but up to 10% show the 'opposite' pattern, so ANCA type supports rather than defines the diagnosis.

GPA triad: upper respiratory tract + lower respiratory tract + kidney. A patient with recurrent 'sinusitis', a lung infiltrate, palpable purpura and haematuria should be tested for ANCA. MPA is distinguished from GPA by the absence of granulomatous inflammation in the upper respiratory tract and by pulmonary capillaritis.

IgA vasculitis is the commonest vasculitis of childhood, affecting about 20 per 100,000 children per year, and is rare in adults. It is an immune-complex small-vessel vasculitis: galactose-deficient IgA1 and anti-IgA1 antibodies form complexes that deposit in vessel walls. It is commoner from September to April and often follows group A streptococcus, parainfluenza or parvovirus B19 infection.

Chronic hepatitis C accounts for 70–90% of mixed cryoglobulinaemic vasculitis. Features: palpable purpura, arthralgia, neuropathy and membranoproliferative glomerulonephritis; complement (especially C4) is low. Blood must be collected and kept at 37 °C or the cryoglobulins precipitate and the test is falsely negative.

Behçet disease is a variable-vessel vasculitis strongly linked to HLA-B51 and commonest along the ancient Silk Road. It causes recurrent painful oral aphthae, genital ulcers, uveitis (often panuveitis), erythema nodosum, vascular thrombosis and pathergy (a sterile pustule at a needle-prick site). In the ICBD score, oral ulcers, genital ulcers and eye lesions score 2 points each; 4 or more confirms the diagnosis.

Any vasculitis can begin with constitutional symptoms — fever, weight loss, malaise and fatigue — so the hardest step is thinking of it at all. StatPearls advises suspecting vasculitis when systemic symptoms combine with dysfunction of one or more organs, or when a 'pneumonia' or 'sinusitis' keeps relapsing and then a purpuric rash or haematuria appears. Use the organ pattern and the patient's age to narrow the list.

• Kawasaki is medium-vessel (not small) and is the classic cause of coronary aneurysm in children.
• PAN kidney disease is arterial (renal artery vasculitis, infarcts, malignant hypertension) or non-glomerular — unlike the glomerulonephritis of the ANCA vasculitides.
• MPA has no granulomas; GPA and EGPA do.
• EGPA is ANCA-positive in only 30–40% — a negative ANCA does not exclude it.
• IgA vasculitis needs purpura without thrombocytopenia — low platelets point elsewhere.
• Cryoglobulin sample must be kept warm (37 °C).
• Takayasu diagnosis is by imaging; GCA diagnosis is by temporal artery biopsy (or ultrasound halo sign).