How are vasculitic disorders defined and classified?

Vasculitis is defined as inflammation of blood vessels. Vasculitis may be confined to the skin; however, the majority of cases of cutaneous vasculitis are part of multisystemic disorders that in addition to involving skin also involve other organ systems. Classification is problematic due to the lack of standardization and definition. The most accepted classification scheme for systemic vasculitis syndromes is based on the size of the involved blood vessels, as shown in Table 15-1. Subclassification of these syndromes is based on clinical and histologic criteria that have been determined to be suggestive of a specific disorder. The American College of Rheumatology Subcommittee on Classification of Vasculitis has determined classification criteria for many of these disorders (see Table 15-1). This classification system is excellent for systemic vasculitis but it omits some forms of vasculitis that are confined to the skin.

Table 15-1. Classification of Systemic Vasculitides
	VESSEL SIZE		VASCULITIC SYNDROME
	Large vessel vasculitis		Giant cell (temporal) arteritis Takayasu arteritis
	Medium vessel vasculitis		Polyarteritis nodosa (classic PAN) Kawasaki disease
	Small vessel vasculitis		Wegener’s granulomatosis Churg-Strauss syndrome Microscopic polyangiitis (polyarteritis) Henoch-Schönlein purpura Essential cryoglobulinemic vasculitis Cutaneous leukocytoclastic vasculitis
	Adapted from Jennette JC, Falk RJ, Andrassy K, et al: Nomenclature of systemic vasculitides: proposal of an International Consensus Conference, Arthritis Rheum 37:187–192, 1994. Adopted by the Chapel Hill Consensus Conference on the Nomenclature of Systemic Vasculitis, 1994.