The commonest vasculitides are giant cell arteritis and Kawasaki disease. Despite their rarity, the medium and small vessel vasculitides are important diagnoses to be familiar with: as multi-system diseases they are great mimics, and their consequences may be life-threatening.

Medium vessel vasculitis

Polyarteritis nodosa

This necrotising vasculitis leads to aneurysm formation and predominantly involves vessels supplying the peripheral nerves, intestinal tract, kidney, skin and joints. Symptoms include constitutional upset, myalgias, orchitis and ischaemia (leading to vasculitic rashes, mononeuritis multiplex, renal failure, abdominal pain and coronary artery disease). It is associated with a marked inflammatory response and there is evidence of previous hepatitis B infection in up to 40% cases.

Diagnosis is by angiography, which reveals microaneurysms in the renal arterial tree and occlusions and irregular visceral arteries.

Kawasaki disease

This affects children, causing fever, conjunctival injection, fissuring/crusting of the lips, strawberry tongue, lymphadenopathy, erythema and desquamation of the hands. The vasculitis can affect all organs but the most feared complication is coronary arteritis. The first investigation of choice is therefore echocardiography to rule out cardiac involvement.

Small vessel vasculitis

The small vessel vasculitides are subdivided according to their association with anti-neutrophil cytoplasm antibodies. The ANCA-positive vasculitides are further subdivided according to staining patterns: cytoplasmic staining (cANCA) is directed against proteinase 3 and is classically associated with Wegener’s granulomatosis while perinuclear staining (pANCA) is directed against myeloperoxidase and is classically associated with microscopic polyangiitis. The cANCA / pANCA division is not clear-cut and not a consistent rule; in addition, ANCAs on their own do not constitute a diagnosis of vasculitis.