Comparing clinical outcomes of rheumatoid arthritis by onset type: palindromic rheumatism, undifferentiated arthritis, and typical rheumatoid arthritis.

objectiveRheumatoid arthritis (RA) evolves through a preclinical phase to clinical phase. At this phase, patients may experience only mono- or oligoarthritis or transient joint episodes, classified as undifferentiated inflammatory arthritis (UIA) or palindromic rheumatism (PR). This prospective study compared the clinical features and outcomes of RA in individuals who had experienced transient episodes of arthritis, or UIA, before being diagnosed with RA, with those who fulfilled RA classification criteria at first presentation.

methodCases from three prospective cohorts of RA, PR, and UIA were enrolled. Patients from the PR and UIA cohorts were included in this study if they fulfilled the classification criteria for RA during follow-up.

resultsCompared with typical-onset RA, patients with palindromic-onset RA were younger and had a higher prevalence of family history of rheumatic diseases, more frequent knee and shoulder joint involvement, and a higher frequency of anticitrullinated protein antibody positivity, but less frequency of morning stiffness and lower disease activity at the time of diagnosis. Patients with UIA-onset RA were more likely to be female, had more frequent knee joint involvement, less frequent morning stiffness, and lower disease activity at the time of diagnosis, compared with patients with typical-onset RA. Although the palindromic-onset group achieved remission significantly earlier than the other groups, no significant differences were observed among the three groups in other outcomes.

conclusionsOur findings suggest that only a subset of PR and UIA patients progress to established RA, and that these entities may represent heterogeneous conditions with overlapping but distinct immunopathogenic mechanisms. Key Points • Rheumatoid arthritis starts with episodic arthritis and undifferentiated arthritis in 9.9% and 7.4% of patients, respectively. • Patients with palindromic-onset rheumatoid arthritis are younger, have a higher prevalence of family history of rheumatic diseases, more frequent knee and shoulder joint involvement, and a higher frequency of ACPA positivity. • Patients with undifferentiated arthritis onset RA are more likely to be female and have more frequent knee joint involvement, less frequent morning stiffness, and lower disease activity at the time of diagnosis. • Poor articular outcome is less frequent in the palindromic-onset rheumatoid arthritis.