Emerging evidence on the response of RA to early treatment suggests the existence of a window of opportunity in RA, a time during which effective therapy can lead to long-term benefits in outcomes, including a sufficient reduction in disease activity so that existing criteria for RA may not be met. Because these findings point to the need for early treatment, the goals of the criteria appear to have changed from classification criteria to diagnostic criteria. Classification criteria need to identify patients with RA correctly to minimize misclassification in clinical or epidemiological studies. In contrast, diagnostic criteria should allow the clinician to reach a diagnosis when confronted with a given patient in the clinic. Thus, at the present time, to meet the clinical needs of improving outcomes by prompt DMARD therapy, diagnostic tools are required to identify patients with RA at the earliest stages of disease.
The difficulty in developing criteria for RA can be handled in two ways. First, new criteria can be derived, and these criteria can function as both classification criteria and diagnostic criteria for early RA. Alternatively, the definition of RA ascertained in the 1987 ACR classification criteria can remain unchanged, although methodology can be developed to identify those patients with early arthritis who will develop RA (see Table 2, p. 24). Both options have advantages and disadvantages that will be considered here.
Rheumatologists now know the importance of treating early disease … . The purpose of these revised criteria is increased sensitivity and specificity to diagnose RA in an early phase of disease.
Developing New Criteria
New criteria for RA have been developed by a task force composed of rheumatologists from the United States and Europe, resulting in the ACR/European League Against Rheumatism (EULAR) Classification Criteria.2–4 These new criteria have been developed in two phases. In the first phase, patient characteristics associated with methotrexate treatment were identified using several European and Canadian early arthritis cohorts. Methotrexate prescription during the first year after diagnosis was chosen as an indication of RA. In the subsequent phase of criteria development, the knowledge and experience of expert clinicians were used to reach a consensus for the final criteria set. The combination of data-driven and expert-driven approaches created a set of criteria that is useful and informative—and is supported by a process that incorporates the “gut feelings” from rheumatologists.
The ACR/EULAR criteria for RA are meant to be applied to persons with undifferentiated inflammatory arthritis (UA).2,4 They can be fulfilled in two ways—either by erosiveness (e.g., joint erosions) on X-rays, or by having a combination of six or more points from the following variables: number of involved joints, localization of involved joints (large or small joints), symmetry, duration of synovitis, acute phase reactants, and RF and ACPA that are both weighed for their level (see Table 2, p. 24). Importantly, this construct indicates that if another definable disease better explains the presence of synovitis, the new criteria for RA should not be applied. This statement implies that, in its new definition, RA is a disease of exclusion that should not be diagnosed if other criteria can be fulfilled as well. As such, this definition is different from ACR criteria for other rheumatologic conditions, in which the absence of fulfilling criteria for other diagnoses are not part of the requirements.
