Definitions and classification of systemic vasculitides

Primary vasculitides can be classified according to the 1990 American College of Rheumatology classification criteria (Arend et al., 1990; Bloch et al., 1990; Fries et al., 1990; Hunder et al., 1990; Leavitt et al., 1990; Lightfoot et al., 1990; Masi et al., 1990; Mills et al., 1990) or to the more accurate and complete Nomenclature of Systemic Vasculitides, established at the Chapel Hill Consensus Conference (Jennette et al., 1994), reproduced in Table 1.

Vasculitides are defined based on their histologic features. Vasculitic lesions (fibrinoid necrosis of vessel walls, perivascular inflammatory infiltrates, fibrotic scar replacement, thromboses) have a segmental distribution pattern, with a predilection for arterial bifurcations, and can cause tissue ischemia and consequential damage. On the other hand, granulomatous inflammation is one of the characteristic features of WG and CSS.

However, because tissues easily accessible to biopsy may show only non-specific inflammation or may even be normal, diagnosis sometimes relies on a combination of clinical findings, and results of biologic, immunologic and radiologic investigations. Anti-neutrophil cytoplasmic antibodies (ANCA) and angiography are useful tools to help diagnose systemic necrotizing vasculitides. In immunofluorescence assays, C-ANCA give a cytoplasmic-labeling pattern in ethanol-fixed ne-utrophils and are detected in 60-90% of the patients with systemic WG, and in 50-75% of those with localized forms of WG (Kallenberg et al., 1992; van der Woude et al., 1985). P-ANCA, which give a perinuclear immunofluorescent labeling pattern, are more closely linked to pauci-immune glomerulonephritis (80% of the patients), microscopic polyangiitis (MPA; 50-75%) and CSS

Table 1

Names and definitions of vasculitides adopted by the Chapel Hill Consensus Conference on the nomenclature of systemic vasculitidesa

Large vessel vasculitis Giant cell (temporal) arteritis

Takayasu's arteritis

Medium-sized vessel vasculitis Polyarteritis nodosa

Kawasaki disease

Small vessel vasculitis Wegener's granulomatosisb

Churg—Strauss syndromeb Microscopic polyangiitisb

Henoch-Schonlein purpura

Essential cryoglobulinemic vasculitis

Cutaneous leukocytoclastic angiitis

Source: Reproduced with permission from Jennette et al. (1994) a Large vessel refers to the aorta and the largest branches directed toward major body regions (e.g., to the extremities and the head and neck); medium-sized vessel refers to the main visceral arteries (e.g., renal, hepatic, coronary and mesenteric arteries); small vessel refers to venules, capillaries, arterioles and the intraparenchymal distal arterial radicals that connect with arterioles. Some small and large vessel vasculitides may involve medium-sized arteries, but large and medium-sized vessel vasculitides do not involve vessels smaller than arteries. Essential components are represented by normal type; italicized type represents usual, but not essential, components. b Strongly associated with antineutrophil cytoplasmic autoantibodies.

Granulomatous arteritis of the aorta and its major branches, with a predilection for the extracranial branches of the carotid artery. Often involves the temporal artery. Usually occurs in patients older than 50 and often is associated with polymyalgia rheumatica. Granulomatous inflammation of the aorta and its major branches. Usually occurs in patients younger than 50.

Necrotizing inflammation of medium-sized or small arteries without glomerulonephritis or vasculitis in arterioles, capillaries or venules.

Arteritis involving large, medium-sized, and small arteries, and associated with mucocutaneous lymph node syndrome. Coronary arteries are often involved. Aorta and veins may be involved. Usually occurs in children.

Granulomatous inflammation involving the respiratory tract, and necrotizing vasculitis affecting small to medium-sized vessels (e.g., capillaries, venules, arterioles and arteries). Necrotizing glomerulonephritis is common.

Eosinophil-rich and granulomatous inflammation involving the respiratory tract, and necrotizing vasculitis affecting small to medium-sized vessels, and associated with asthma and eosinophilia. Necrotizing vasculitis, with few or no immune deposits, affecting small vessels (i.e., capillaries, venules, or arterioles). Necrotizing arteritis involving small and medium-sized arteries may be present. Necrotizing glomerulonephritis is very common. Pulmonary capillaritis often occurs. Vasculitis with IgA-dominant immune deposits, affecting small vessels (i.e., capillaries, venules or arterioles). Typically involves skin, gut and glomeruli, and is associated with arthralgias or arthritis. Vasculitis, with cryoglobulin immune deposits, affecting small vessels (i.e., capillaries, venules, or arterioles), and associated with cryoglobulins in serum. Skin and glomeruli are often involved. Isolated leukocytoclastic angiitis without systemic vasculitis or glomerulonephritis.

(47%) (Hagen et al., 1998). Celiomesenteric and renal angiographic findings, such as multiple 1-5-mm diameter aneurysms or irregular stenoses are present in approximately 80% of PAN patients (D'Izarn et al., 1976; Guillevin et al., 1995a). Although highly suggestive, these findings are not absolutely specific and, to date, no diagnostic criteria for vasculitides have been established.

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