Pos0800 Biologic Disease-Modifying Antirheumatic Drugs Survival in Late-Onset Axial Spondyloarthritis – Data From a Multicentre Nationwide Study

Background: Axial spondyloarthritis (axSpA) symptoms usually begin before the age of 45. However, due to longer life expectancy and improved healthcare, late-onset axSpA (Lo-axSpA) is becoming more recognized. Previous studies have shown different clinical characteristics between the late and early onset (Eo) forms of the disease. Nonetheless, there is limited data available on the efficacy of biological disease-modifying antirheumatic drugs (bDMARDs) in Lo-axSpA. Objectives: To evaluate drug survival of bDMARDs in Lo-axSpA patients compared to those with Eo-axSpA. Methods: We performed a retrospective multicenter national cohort study on patients with a diagnosis of axSpA, registered in Reuma.pt, the Portuguese registry of patients with rheumatic diseases. Adult patients who were clinically diagnosed with axSpA by their rheumatologist and had available information on the age of symptom onset were included. The patients were divided into 2 groups based on their age at symptom onset: Eo-axSpA (<45 years) and Lo-axSpA (≥45 years). Non-parametric tests were used to evaluate the group differences. Drug survival was calculated as the time in months from the initiation of bDMARD until its discontinuation/switch and the log-rank test was used to calculate the persistence rate in biological treatment. R software version 4.3.2 was used, and a p ≤ 0.05 was considered statistically significant. Results: A total of 1953 patients (1703 with Eo-axSpA and 250 with Lo-axSpA) were included. The Lo-axSpA group had a higher body mass index (BMI), higher prevalence of inflammatory bowel disease and lower prevalence of acute anterior uveitis, HLA-B27 positivity and SpA family history. Lo-axSpA were more likely to have higher disease-associated parameters at baseline, 6, and 12 months of bDMARD therapy (Table 1). The drug retention rate was lower in Lo-axSpA and the survival analysis showed a higher probability of discontinuing treatment in this group (HR 1.50 (1.20-1.88), p<0.001). When adjusting for confounders, the Lo-axSpA group had no significant differences in treatment persistence. However, a higher age of disease onset increased the risk of discontinuing therapy by 2% (HR 1.02 (1.01-1.04), p=0.001). Being male (HR 0.77 (0.65-0.92), p=0.004), HLA-B27 positivity (HR 0.80 (0.67-0.95), p=0.01) and higher CRP levels (HR 0.80 (0.66-0.96), p=0.02) were associated with a lower risk of discontinuing therapy, while having a good response to NSAIDs (HR 1.22 (1.01-1.45), p=0.03) and higher BMI (1.02 (1.00-1.04), p=0.02) were associated with an increased risk. Regarding bDMARD therapy, patients who were on etanercept (HR 0.92 (0.50-0.78), p=<0.001), infliximab (HR 0.69 (0.53-0.90), p=0.006) and golimumab (HR 0.75 (0.58-0.97), p=0.03) had a lower risk of discontinuing therapy compared to the adalimumab reference group. Conclusion: Based on real-world nationwide data, we found that bDMARDs had lower clinical efficacy in patients with Lo-axSpA, with shorter drug retention time. Although Lo-axSpA itself was not a significant factor in predicting drug discontinuation, age at disease onset was associated with a higher risk of discontinuation. Additionally, HLA-B27 absence, female gender and higher BMI were also linked to a higher risk of therapy discontinuation. Even though it represents a minority, clinicians should be aware of this phenotype, since it can be associated with a higher clinical burden and lower treatment efficacy. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.