Systemic necrotizing vasculitis.

Systemic necrotizing vasculitis may be idiopathic or associated with a variety of diseases of known etiology. A typical example is polyarteritis nodosa, which is characterized by fibrinoid necrosis and severe inflammation leading to destruction of the wall, narrowing of the lumen, and interference with blood circulation. In addition to the idiopathic form, histologically similar lesions are seen in hepatitis B, rheumatoid arthritis, Kawasaki mucocutaneous lymph node syndrome, and other diseases. Microscopic polyangitis involves mainly small vessels-venules more often than arterioles-but occasionally also small arteries. Its characteristic feature is leukocytoclasia of neutrophilic leukocytes, but fibrinoid necrosis also occurs. Churg-Strauss syndrome consists of granulomas in patients with a background of severe allergy, such as asthma, allergic rhinitis, or occasionally drug sensitization.