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.

Patients with leukocytoclastic vasculitis, also referred to as leukocytoclastic angiitis and allergic or necrotizing vasculitis, present with characteristic purpuric papules, most frequently involving the extremities, known as palpable purpura (Fig. 15-1). Biopsies of cutaneous leukocytoclastic vasculitis demonstrate an intense perivascular infiltrate composed of intact and fragmented neutrophils (nuclear dust) that focally infiltrate the vessel wall producing fibrinoid changes and/or necrosis. These damaged vessels frequently demonstrate extravasation of erythrocytes and may also demonstrate thrombosis.

Kluger N, Francès C: Cutaneous vasculitis and their differential diagnoses, Clin Exp Rheumatol 27(1 Suppl 52):S124–S138, 2009.

Acute hemorrhagic edema of infancy, which also called “cockade purpura,” is also an IgA-mediated immune complex leukocytoclastic vasculitis that affects small cutaneous vessels. This variant almost always affects young children (median age is 11 months), and like Henoch-Schönlein purpura, it is usually associated with a preexisting upper respiratory infection. It differs in that the primary cutaneous clinical lesions are typically indurated, edematous plaques with variable hemorrhage that are less likely to ulcerate. The lesions frequently affect the head and neck region and extremities (Fig. 15-2). The children typically do not demonstrate significant involvement of the gastrointestinal tract, joints or kidneys and do not develop permanent sequelae.

Fiore E, Rizzi M, Ragazzi M, et al: Acute hemorrhagic edema of young children (cockade purpura and edema): a case series and systematic review, J Am Acad Dermatol 59:684–695, 2008.