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Necrotizing angiitis or vasculitis comprises a diverse group of disorders that combine segmental inflammation with necrosis of the blood vessels. The vascular damage may result from immunologic and/or inflammatory mechanisms. Clinical syndromes are based on criteria that include the gross appearance and the histopathologic alterations of the vascular lesions, the caliber of the affected blood vessels, the frequency of involvement of specific organs, and laboratory abnormalities. Necrotizing vasculitis may be a primary disease, may develop as a feature of a systemic disorder, or may be idiopathic. There is no standard classification of the vasculitides; the American College of Rheumatology classification and the Chapel Hill consensus criteria are widely used.1,2 These classifications are limited in clinical practice, owing to the lack of recognition of certain disorders, the overlap of clinical manifestations, and the lack of precision in the description of cutaneous features.
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Necrotizing vasculitis in the skin predominantly involves venules and is known as cutaneous necrotizing venulitis/vasculitis (CNV), cutaneous small-vessel vasculitis, and leukocytoclastic vasculitis. The occurrence of CNV in association with systemic involvement of the small blood vessels has been termed hypersensitivity angiitis/vasculitis, systemic polyangiitis, and microscopic polyangiitis (see Chapter 164). CNV may be restricted to the skin, may occur in association with an underlying chronic disease, may be precipitated by infections or drugs, or may develop for unknown reasons (Table 163-1). Systemic forms of necrotizing vasculitis that affect larger blood vessels are considered in Chapter 164.
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