The Use and Misuse of Classification and Diagnostic Criteria for Complex Diseases

The vasculitides are a group of complex multi-system disorders that are linked by the presence of necrotizing inflammatory lesions in blood vessels. Arteries and other vessels of various sizes and lo-cations in the body may be involved, resulting in a wide spectrum of manifestations (1). The causes and pathogenetic mechanisms of vasculitides are poorly understood but are probably diverse. Their severity, course, and outcomes vary. Within the vas-culitides, there seem to be several distinct clinical syndromes. However, even these have multiple pre-sentations, and the different syndromes have over-lapping findings. These factors have made it difficult to define these diseases and diagnose individual cases. A tissue biopsy showing arteritis confirms vas-culitis but by itself does not necessarily define