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Segmental, necrotizing inflammation of media and adventitia characterizes the lesion. The pathologic process most commonly occurs at points of vessel bifurcation, beginning in the media and extending into the intima and adventitia of medium-sized arteries, often disrupting the internal elastic lamellae. Lesions usually occur in all stages of development and healing. Early lesions contain PMNs and occasionally eosinophils; later lesions contain lymphocytes and plasma cells. Immunoglobulin, complement components, and fibrinogen are deposited in the lesions, but their significance is unclear. Intimal proliferation with secondary thrombosis and occlusion leads to organ and tissue infarction. Weakening of the muscular vessel wall may cause small aneurysms and arterial dissection. Healing can result in nodular fibrosis of the adventitia.
Renal, hepatic, cardiac, and GI involvement is most frequent.
Renal lesions are of two types: large-vessel (the lesion is a tubular infarction, and renal failure is uncommon) and microvascular, including the glomerular afferent arterioles (the lesion is diffuse, and renal failure is common and occurs early).
Of patients with massive hepatic infarction, 50% have polyarteritis nodosa, although this complication is rare.
Milder degrees of hepatic tenderness and increased concentrations of liver enzymes usually reflect focal areas of hepatic capsular vasculitis.
Several polyarteritis nodosa-associated syndromes are separated from typical polyarteritis nodosa by pathogenic or clinical differences:
hypersensitivity angiitis; Churg-Strauss syndrome (the vasculitis includes lung involvement, eosinophilia, necrotizing granulomas, and severe asthma); Cogan's syndrome (the disease begins as interstitial keratitis and inner ear infarction); pure mesenteric polyarteritis nodosa (recognized in IV methamphetamine addicts); Kawasaki's disease (mucocutaneous lymph node syndrome in infants and children complicated by coronary arteritis with early aneurysm formation); and necrotizing arteritis associated with hepatitis B infection (either acute hepatitis or chronic active liver disease). Many patients with essential cryoglobulinemia causing small- and medium-sized vasculitis (ie, palpable purpura, digital vessel occlusion, glomerulonephritis) are chronically infected with hepatitis C.
The interrelationships of idiopathic polyarteritis nodosa and these forms of arteritis are unclear.
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