Early arthritis clinics will consist of a very heterogeneous group of arthritis patients, both as to their initial clinical presentation as to their outcome. Dependent on the way patients have been selected, about one third of the patients has a disease that may ultimately classified as rheumatoid arthritis (RA), one third will have another classifiable inflammatory rheumatic disorder and one third of the patients remains unclassified.
The diagnosis or classification of RA is based on the presence of a distinct clinical entity that needs a certain amount of time to develop. The classification criteria for RA are therefore not very suitable for early diagnosis. In addition, there is a certain circularity in using the ACR criteria as gold standard to diagnose RA early in the disease course. The essence of RA diagnosis or RA classification is the presence of a persistent and destructive polyarthritis. In early arthritis we are not dealing with an already existing disease entity that can be classified as RA, but we are confronted with a very heterogeneous patient population. At that stage we would like to predict which patients will have a self-limiting arthritis, a persistent non-erosive arthritis or a persistent erosive arthritis. At present Ig-M rheumatoid factor (RF) appears to be the most powerful single predictor of persistent erosive arthritis. Apart from genetic markers, many clinical and laboratory parameters at the beginning of the disease have been found more or less predictive of severe erosive arthritis, including active polyarthritis, high scores of disease activity measurements, involvement of at least two large joints, different serological markers such as the anti-perinuclear factor (APF) and anti-citrulline antibodies (Anti-CCP, “AKA”), initial HAQ score and initial radiological score. None of these variables is powerful enough though, to predict the presence of persistent erosive arthritis as a single predictor. Analysis of the Leiden Early Arthritis Cohort data showed that, looking at all potentially predictive determinants obtained from patient history, physical examination, serological and genetic markers, an optimal criteria set of 7 variables consisting of symptom duration, morning stiffness >1 h, arthritis of 3 or more joints, bilateral compression pain of metatarsophalangeal joints, RF positivity, anti-cyclic citrullinated peptide antibody positivity and the presence of erosions could successfully discriminate between self-limiting, persistent non-erosive and erosive arthritis. The predictive model could be simplified to provide predictive probabilities at the individual patient level. The overall diagnostic/prognostic performance of the 1987 ACR classification criteria was significantly lower than the criteria set described above. The utility of (a combination of) diagnostic/predictive parameters has to be judged against the background of the patient population in which the criteria have been developed.
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