Vasculitis—classification and diagnosis
The vasculitides are a group of conditions characterized by inflammation and necrosis of blood vessels; they are generally of unknown aetiology. The classification of vasculitides is based on the size of vessel involved and whether there is a known cause (secondary) or not (primary). This approach has stood the test of time. The American College of Rheumatology (ACR) in 1990 produced classification criteria for the major types of vasculitis and in 1994 definitions were promulgated by the Chapel Hill Consensus Conference. These did not include anti-neutrophil cytoplasm antibodies (ANCA) and the ACR scheme did not include microscopic polyangiitis. The definitions have recently been updated to include modern concepts of pathogenesis including ANCA. No validated diagnostic criteria are available for routine clinical practice. The diagnosis of vasculitis requires a high index of suspicion, especially in the systemically unwell patient with multiorgan involvement. The key to diagnosis is a detailed and systematic approach to patient assessment involving all potentially involved organs. In a patient with suspected vasculitis immediate urinalysis is mandatory as the severity of renal involvement at presentation is a major determinant of outcome. Each potentially involved organ should be comprehensively evaluated. Tissue biopsy should be obtained whenever possible, as treatment is potentially toxic using glucocorticoids combined with cytotoxic agents. Biopsy should not, however, delay initiation of treatment. Potential alternative diagnosis should be considered, especially infection and malignancy, and excluded whenever possible.