Patients with undifferentiated arthritis (UA) that is defined according to contemporary criteria don’t appear to have the same excess mortality that is associated with rheumatoid arthritis, despite links between the two conditions.
UA has long been considered an earlier phase of RA, so similar management strategies are often used based on the assumption that outcomes and elevated mortality risk were similar between the two, but new findings reported in a research letter published in Annals of the Rheumatic Diseases challenge that assumption.
The change in the definition of UA that accompanied the introduction of new RA criteria in 2010 meant that some of the patients who previously met the criteria for UA now were classified as having RA, and “the remaining contemporary UA population (not fulfilling the 1987/2010 RA criteria) is largely autoantibody negative, presents with monoarthritis or oligoarthritis, and progresses less frequently to RA,” PhD candidate Marloes Verstappen of Leiden (Netherlands) University Medical Center, and coauthors wrote.
As the first large study on excess mortality in patients meeting contemporary criteria for UA, the authors said it suggests that the change in criteria for UA has served to increase the differences in mortality between it and RA.
“Further research and discussions are needed as to whether the management of contemporary UA should be similar to or different from that of RA,” they wrote.
The researchers conducted a longitudinal cohort study of 860 patients who met the conventional criteria for UA – they did not meet the 1987 RA criteria or other diagnosis – at baseline and 561 who met contemporary criteria for UA based on the fact that they did not meet the 1987 or 2010 RA criteria. There were also 762 patients who were diagnosed with RA according to the 1987 criteria, and 828 diagnosed according to the 2010 criteria. All of these patients were diagnosed between 1993 and 2008 and their median follow-up times ranged from 16.0 to 17.3 years, with a minimum of 10 years of follow-up.
The study found that, while there was a trend toward excess mortality in the conventional UA group (standardized mortality ratio, 1.11; 95% confidence interval, 0.96-1.27), there was no significant excess mortality in the contemporary UA patients (SMR, 1.05; 95% CI, 0.87-1.26).
In comparison, patients in both the 1987 RA criteria group and the 2010 criteria group showed significantly higher mortality. Among patients with anti–citrullinated protein antibody–positive disease, even early treatment with disease-modifying antirheumatic drugs and treat-to-target strategies didn’t reduce the excess mortality.
The study did find some suggestion of excess mortality among patients with contemporary UA and who were anti–citrullinated protein antibody positive, but the number of patients was small.
“Only a few percent of patients presenting with contemporary UA are autoantibody positive; these patients may be considered at increased risk to progress to RA,” the authors wrote.
The data also suggested that disease-modifying antirheumatic drugs didn’t alter excess mortality among patients with contemporary UA.
The study was supported by the Dutch Arthritis Foundation and the European Research Council. No conflicts of interest were declared.