96 - Immune Complex–Mediated Small Vessel Vasculitis

Abstract

Vasculitis mediated by immune complexes (ICs) includes a heterogeneous group of disorders linked by excess IC production or by inefficient or dysregulated clearance of ICs. The most common types of IC-mediated vasculitis are hypersensitivity vasculitis, immunoglobulin (Ig)A vasculitis (formerly Henoch-Schönlein purpura [HSP]), and mixed cryoglobulinemia. Rarer forms of this condition include hypocomplementemic urticarial vasculitis, erythema elevatum diutinum, and IgG4-related disease. Connective tissue disorders such as systemic lupus erythematosus, Sjögren’s syndrome, and rheumatoid arthritis can be associated with IC-mediated vasculitis. Cutaneous involvement of small blood vessels is the most prominent feature in the majority of cases, but extracutaneous involvement occurs in some forms. The classic cutaneous finding in small vessel vasculitis is palpable purpura, but a variety of other skin lesions may also be found. Other types of skin lesions associated with IC-mediated small-vessel vasculitis include pustules, vesicles, urticaria, and small ulcerations. Direct immunofluorescence studies of involved blood vessels demonstrate characteristic types and patterns of Ig and complement deposition. Hypersensitivity vasculitis usually results from a reaction to a medication or an infection. The syndrome of hypersensitivity vasculitis includes two terms from the second Chapel Hill Consensus Conference: drug-induced IC-mediated vasculitis and cutaneous leukocytoclastic angiitis. IgA vasculitis (Henoch-Schönlein purpura) is associated with purpura, arthritis, glomerulonephritis, and colicky abdominal pain. IgA deposition is found within blood vessel walls. Cryoglobulinemic vasculitis is most often associated with long-standing hepatitis C virus infection. The term mixed cryoglobulinemia is sometimes used for this disorder because the immunoreactants involved in the disease include both IgG and IgM.