Distinctions Between Diagnostic and Classification Criteria?

Rheumatologists face unique challenges in discriminating between rheumatologic and non-rheumatologic disorders with similar manifestations, and in discriminating among rheumatologic disorders with shared features. The majority of rheumatic diseases are multisystem disorders with poorly understood etiology; they tend to be heterogeneous in their presentation, course, and outcome, and do not have a single clinical, laboratory, pathological, or radiological feature that could serve as a “gold standard” in support of diagnosis and/or classification. Thus, the development of criteria for use in routine clinical care and in clinical research has been an important focus in rheumatology. Improved understanding of disease pathogenesis and new diagnostic tools have led to reexamination of existing classification and diagnostic criteria with updated classification criteria for some diseases being endorsed recently (1, 2). The American College of Rheumatology (ACR) Subcommittee on Classification and Response Criteria is responsible for guiding the development and validation of new classification and response criteria that are eventually considered for ACR endorsement. This includes review of proposals for the development of new criteria sets and providing the ACR leadership with recommendations for development and approval of new classification and response criteria sets (1, 3–5). The Subcommittee has previously published a guidance paper for the development of classification and response criteria (6). This prior work has provided details about the rationale for the ACR’s position on classification criteria, but clarification around the issue of diagnostic criteria was lacking. Indeed, the ACR endorsed preliminary diagnostic criteria for fibromyalgia (7) in 2010, which prompted discussions about whether the Subcommittee should also support the development and ACR endorsement of diagnostic criteria, in addition to that of classification and response criteria. The primary objectives of this current article, by former and current members of the Subcommittee on Classification and Response Criteria, are to compare diagnostic and classification criteria, using specific examples from the published literature, and to clarify the ACR’s position on both types of criteria.