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Two decades ago, the terminology of undifferentiated arthritis (UA) was proposed with the hypothesis that UA is an earlier phase of rheumatoid arthritis (RA).1 Consequently, management strategies of RA are often transferred to UA-patients, assuming outcomes are comparable. Mortality is a long-term outcome that is unknown in UA, but widely studied in RA.
In RA, excess mortality becomes apparent after 10 years of follow-up in both anticitrullinated protein antibody (ACPA)-negative and ACPA-positive RA, and is presumably mediated by long-term, insufficiently suppressed inflammation.2–4 Recently, it has been shown that early and treat-to-target treatment resolved excess mortality in ACPA-negative-RA, but not in ACPA-positive-RA.5 In UA, mortality rates are unknown. Moreover, the UA-population has changed during the last decade.1 Conventionally, UA was defined as not fulfilling the 1987 RA-critera and absence of another clinical diagnosis. With the introduction of the 2010 RA-criteria, part of the conventional UA- population became classified as RA. 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monoarthritis or oligoarthritis and progresses less frequently to RA.6 Thus, this population of contemporary UA may no longer represent a group of patients in an early phase of RA, but a population with intrinsically different characteristics than RA. We, therefore, hypothesised that there is no excess mortality in contemporary UA, in contrast to RA. This prompted us to assess mortality-rates in contemporary …
Handling editor Josef S Smolen
Contributors All authors contributed to the conception and study design. MV contributed to acquisition of the data and analysed the data. All authors contributed to interpretation of the data and the development of the manuscript. All authors approved the final version of the manuscript.
Funding The research leading to these results has received funding from the Dutch Arthritis Foundation and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (starting grant, agreement No 714312).
Disclaimer The funding source had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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