Ab0611 Predictors of Ra Development in Patients With Acpa Positive Undifferentiated Arthritis: A 2 to 20 Years Follow-Up Study of the Arthritis Uclouvain Brussels Cohort

Background: Patients with Undifferentiated Arthritis (UA), positive for Anti-citrullinated protein antibodies (ACPA) are at high risk of progressing to Rheumatoid Arthritis (RA). However, some of them may experience spontaneous remission. To prevent overtreatment and potential side effects, the identification of predictors of RA development is crucial. Objectives: This research aims to analyze the evolution of UA patients with ACPA evolving RA or not after 2 to 20 years of follow-up and to determine the predictive factors. Methods: A prospective analysis of an early arthritis cohort of 700 patients from 2003 to 2021 was analyzed. Among them, UA was defined if they did not fulfill the 1987 ACR and the ACR/EULAR 2010 criteria. Patients with baseline erosion or joint space narrowing were excluded from the study. A detailed baseline assessment was performed including all clinical characteristics and the ACR/EULAR score set components. ACPA UA patients were divided into two groups based on the progression to RA (according to the physician's diagnosis) and the initiation of Methotrexate. All csDMARDs were prohibited during the follow-up of UA. Differences in continuous variables between the two groups were analyzed by T-test or Mann-Whitney test depending on normality. Levene's test was used to analyze the equality of variance. Chi-squared or Fisher's exact test was applied to analyse the significance of the association between categorical variables. Spearman's correlation test was used to assess the presence of significant correlations between variables. Results: A total cohort of 96 ACPA UA patients was analyzed. 35 patients (36.4%) were still defined as UA during the last follow-up visit and 61 (63.6%) developed RA after a mean follow-up of 2 years ± 2.09. Baseline characteristics between both groups are compared in Table 1. At baseline, ACPA UA patients who developed RA had significantly more small-TJC (0.43 ± 0.9 versus 1.3 ±2.0; p=0.004), small-SJC (0.1 ± 0.2 versus 0.5 ± 0.9; p=0.001) and ACR/EULAR 2010 score (4.3 ± 0.8 versus 5.1 ± 1.3; pTable 1. Baseline comparison of UA and RA Cohort. Conclusion: We confirm that ACPA UA patients are at high risk of developing RA. Baseline evaluation of the ACR/EULAR 2010 including the number of tender and swollen of small joints score is a predictor for RA. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.