Objective Undifferentiated arthritis (UA) is a diagnosis ‘per exclusionem’. Therefore this patient population may change since the development of the ACR/EULAR 2010-criteria for RA. This study evaluated characteristics and outcomes of UA in its new shape. Second, it was evaluated whether the 2010-criteria and the Leiden prediction rule were congruent in categorizing UA-patients.
Methods 2,472 early arthritis patients were studied. RA was classified according to either the 1987 or the 2010-criteria. UA was defined as not fulfilling existing classification criteria. UA-patients were compared for baseline characteristics and outcomes. In 1987-UA-patients both the 2010-criteria and the Leiden prediction rule were applied and categorization compared.
Results 2010-UA-patients (n=776) had milder baseline characteristics than 1987-UA-patients (n=1,166). During follow-up, still 24% of the 2010-UA-patients fulfilled the 1987 RA-criteria compared to 32% of the 1987-UA-patients. The 2010-UA-patients started less frequent DMARD-therapy and reached more frequent sustained DMARD-free remission. 30% of 2010-criteria-positive patients were predicted to have a low risk on RA; these patients achieved more frequent DMARD-free sustained remission than other 2010-criteria-positive patients.
Conclusion UA in the era of the 2010-criteria is less prevalent and milder at presentation and in outcome. This implies that UA-patients with unfavorable characteristics are now more often classified as RA.
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Funding The work of AK is supported by a grant from the Dutch Arthritis Foundation. The work of AHMvdHvM is supported by a grant from the Dutch organisation of Health Research and Development. The research has been funded by the European Community Seventh Framework Program FP7 Health-F2-2008–223404 (Masterswitch) and by a core grant from the Dutch Arthritis Foundation.
Competing interests None.
Patient consent Obtained.
Ethics approval The study was approved by the local medical ethics committee.
Provenance and peer review Not commissioned; externally peer reviewed.