Vasculitis affecting the kidney.

Vasculitis refers to vessel wall leukocyte infiltration, often with necrosis, and can involve any of one or more vessels in the body. The kidney is commonly affected by vasculitis. Vasculitis is best classified based on the size of the involved vessels into large, medium, and small vessel disease. Small vessel vasculitis (SVV) that includes glomerulonephritis is by far the most frequent vasculitic lesion in the kidney, and the defining renal lesion is a necrotizing crescentic glomerulonephritis. Medium vessel vasculitis occasionally involves the kidney as necrotizing arteritis, and large vessel vasculitis only rarely affects the kidney, and most often secondarily by ischemia from proximal arterial narrowing. In this review, we describe the clinical and pathologic features of the various vasculitides that affect the kidney, with emphasis on SVV, particularly the type that is associated with anti-neutrophilic cytoplasmic antibodies (ANCA). We will also discuss the relevance of ANCA and describe evidence supporting the pathogenic role of these antibodies. It is important to remember that a histopathologic vasculitic lesion can be shared by several vasculitides, so that clinical data are most often required for disease classification.