POS1069 REVISING ILAR SUBTYPES OF JUVENILE IDIOPATHIC ARTHRITIS IN ADULTS: A SINGLE CENTER RETROSPECTIVE STUDY

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Background: Juvenile Idiopathic Arthritis (JIA) is the most common chronic rheumatic disease in childhood, and up to one-third of patients continue to experience episodes of active inflammation into adulthood. The International League of Associations for Rheumatology (ILAR) classifies JIA into several subtypes, each of them with distinct clinical and demographic characteristics. Understanding these subtypes is crucial for optimizing patient management and outcomes. The use of biological drugs has brought about a significant change in disease control and improvement of disability in these patients. Previous studies suggest that the response to biological treatment in JIA is influenced by factors such as the subtype of disease, the age at treatment initiation, and prior therapeutic regimens. This variability underscores the need for a better understanding of clinical and demographic characteristics to refine treatment strategies and improve long-term outcomes in JIA patients transitioning into adulthood. Objectives: To perform a descriptive analysis of the clinical and demographic characteristics, treatment patterns, and therapeutic outcomes of the different ILAR subtypes in our cohort. To evaluate the impact of disease duration before initiating biological therapy on treatment efficacy. Methods: We conducted a retrospective cross-sectional observational study involving adult patients diagnosed with JIA who were under follow-up at a tertiary hospital in Spain between 1960 and 2024. Sociodemographic, clinical, and laboratory variables were collected. Systemic JIA was excluded due to its distinct characteristics and the limited number of cases in the cohort, which precluded meaningful statistical analysis. The main variable to assess the response to treatment was the number of biologics received. To analyze the primary outcome, a multiple linear regression model was performed to evaluate the relationship between the years of disease progression at the start of biological therapy and the response to treatment, including potential confounding factors. Additional analyses were performed to evaluate the relationship between disease duration and treatment efficacy, measured by the number of biologics received and the mean survival time of the first biologic. Potential confounding and interaction variables were included in the model. Results: A total of 46 patients were included. The proportion of female patients varied across ILAR subtypes, with a higher prevalence of males in the ERA subtype. The mean age at diagnosis was 9 years old (SD 4,7), being older in the polyarthritis subtype (12 years) and the ERA subtype (11,4 years). Non-steroidal anti-inflammatory drugs (NSAIDs) were the first treatment administered in 56% of the patients. Most patients (76.1%) received a concomitant use of conventional synthetic disease-modifying antirheumatic drugs (csDMARDs). Their clinical and demographic characteristics are displayed in Table 1. Half of the patients received a biological treatment. Their characteristics are described in Table 2. The mean disease duration since biological treatment was 15±14years, and the mean age at the start of the primary biologic was 25±14 years. Patients with polyarticular and oligoarticular subtypes started biological treatment later, at a mean age of 32 and 19 years old, respectively, while patients ERA subtype started earlier, at a mean age of 9 years old. In 96% of the patients, the primary biologic therapy was an anti-TNF, etanercept the most frequent (56%), followed by adalimumab (28%). There were no differences in primary biologic therapy across the ILAR subtypes. The main reason for discontinuing the first biological therapy in patients with the oligoarticular subtype was sustained remission (40%), a finding not observed in other subtypes. The median number of biological lines was equal independent of the ILAR subtype. Multiple linear regression analyses did not demonstrate a conclusive relationship between treatment efficacy and disease duration. Similarly, no statistically significant associations were found between treatment efficacy and other variables, including sex, age at diagnosis, time of diagnosis prior to the biologic era, serologic markers, structural damage at disease onset, the primary biologic agent used, or ILAR subtype. Conclusion: This study highlights the clinical and therapeutical patterns of the ILAR subtypes and identifies outcomes of biological use in a monocentric cohort of adults with JIA. While no statistically significant associations were identified between treatment efficacy and other variables analyzed, the findings underscore the need for further research with larger sample sizes. REFERENCES: [1] Flora McErlane, et al. Biologic Treatment response among adults with juvenile idiopathic arthritis: results from the British Society for Rheumatology Biologics Register. Rheumatology 2013;52:1905-1013. [2] Karen B, et al. 2021 American College of Rheumatology Guideline for the Treatment of Juvenile Idiopathic Arthritis. Arthritis Rheumatol. 2022 April; 74 (4):553-569. Acknowledgements: NIL . Disclosure of Interests: None declared . © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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