Vasculitis

The systemic vasculitides are inflammatory diseases of blood vessel walls that cause narrowing and ischaemia, aneurysm or thrombosis, and are classified by the size of vessel they mainly affect.

They often present to MSK and SEM clinicians with arthralgia, myalgia and constitutional symptoms, and a missed diagnosis can be fatal. Suspect vasculitis when multi-system inflammation comes with palpable purpura, rapidly progressive glomerulonephritis (RPGN), pulmonary haemorrhage, mononeuritis multiplex or unexplained upper airway disease.

Giant cell arteritis (GCA), the most common adult systemic vasculitis, is covered on the PMR and GCA page.

The Chapel Hill 2012 consensus groups the vasculitides by predominant vessel size, which shapes the clinical picture.

Large vessel (aorta and major branches):

• •Giant cell arteritis: granulomatous arteritis in adults over 50
• •Takayasu arteritis: granulomatous aortitis, mainly in young women, more common in Asian populations, causing stenoses, aneurysms and pulse deficits

Medium vessel:

• •Polyarteritis nodosa (PAN): necrotising arteritis with microaneurysms, linked to hepatitis B; ANCA-negative, no glomerulonephritis and no lung involvement
• •Kawasaki disease: childhood vasculitis whose main long-term risk is coronary artery aneurysm

Small vessel, ANCA-associated (pauci-immune):

• •Granulomatosis with polyangiitis (GPA): upper airway, lungs and kidneys; usually c-ANCA (anti-PR3)
• •Microscopic polyangiitis (MPA): kidneys and lungs without granulomas or upper airway disease; usually p-ANCA (anti-MPO)
• •Eosinophilic granulomatosis with polyangiitis (EGPA): asthma, eosinophilia and vasculitis; ANCA-positive in only around 40%

Small vessel, immune complex:

• •IgA vasculitis (Henoch-Schonlein purpura): the most common childhood vasculitis, often after an upper respiratory infection
• •Cryoglobulinaemic vasculitis: linked to hepatitis C

Variable vessel: Behcet's disease (oral and genital ulcers, uveitis, positive pathergy test).

In ANCA-associated vasculitis (AAV), activated neutrophils damage the endothelium with little immune-complex deposition, so complement is usually normal; in immune-complex vasculitis it is often low.