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

The vasculitides are a group of complex multisystem disorders that are linked by the presence of necrotizing inflammatory lesions in blood vessels. Arteries and other vessels of various sizes and locations 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 vasculitides, there seem to be several distinct clinical syndromes. However, even these have multiple presentations, and the different syndromes have overlapping findings. These factors have made it difficult to define these diseases and diagnose individual cases. A tissue biopsy showing arteritis confirms vasculitis but by itself does not necessarily define a specific syndrome [2]. Furthermore, biopsy is a sampling process and sometimes misses an involved vascular segment or provides an incomplete picture of the pathology. In some instances, biopsy may not be feasible. Thus, diagnosis of vasculitis usually depends on the presence of a combination of findings.

Because of the lack of a single pathognomonic test in most rheumatic diseases, including vasculitis, the development of criteria for diagnosis or classification has been of continuing interest to rheumatologists. In the United States, the American College of Rheumatology has taken a lead in developing classification criteria for rheumatic diseases, the main purpose of which is to …