Pos1382 Prevalence and Clinical Characteristics of Late Onset Axial Spondyloarthritis: Results From a Multicentre Nationwide Study

Background: Axial spondyloarthritis (axSpA) typically starts before the fourth decade of life. Consistent with that, the Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axSpA should be applied only in patients with chronic back pain starting before 45 years of age. It has, however, been suggested that axSpA can sometimes start later in life with a distinctive phenotype, the so-called 'late onset axSpA' (lo-axSpA). There is, nevertheless, only limited data in support of the existence of such phenotype. Objectives: We aimed to evaluate the occurrence of lo-axSpA and whether these patients differ from those with early onset axSpA (eo-axSpA). Methods: We performed a cross-sectional, multicentre, nationwide study using data from Reuma.pt, the Portuguese registry of patients with rheumatic diseases. Adult patients with the clinical diagnosis of axSpA, according to their treating rheumatologist, and with available information on the age of symptom onset were included. Lo-axSpA was defined as axSpA with a symptom onset ≥45 years of age. Demographic characteristics (e.g., age, gender, smoking status, and employment), SpA features 12 features (see Table 1) recorded as ever present, i.e., any time in the past or at the current study visit, measures of disease activity (ASDAS and BASDAI), disability (BASFI) and treatment with NSAIDs, csDMARDs and bDMARDs were compared between patients with lo-axSpA and eo-axSpA at the last available visit at the time of data extraction (13/12/2022). The independent association between these patient and disease characteristics with lo-axSpA was tested in a multivariable logistic regression model. The final multivariable model included all variables with a p-value Results: In total, 2165 patients with axSpA were included. The mean (standard deviation; SD) age at symptom onset was 32 (10) years and the mean symptom duration was 17 (12) years. The majority of the patients were male (56%), most had definite damage on pelvic radiographs according to the modified New York criteria (85%) and were treated with bDMARDs (77%). Out of the total 2165 patients, 273 (13%) had symptom onset ≥45 years and were therefore labelled as lo-axSpA. There were no differences in disease activity, disability or treatment between patients with lo-axSpA and eo-axSpA (Table 1). There were, however, some notable differences between the two groups. Patients with lo-axSpA were less often positive for HLA-B27 (51% vs 65%), less likely to have family history of SpA (8% vs 14%), acute anterior uveitis (AAU, 13% vs 20%) and inflammatory back pain (IBP, 81% vs 88%) than patients with eo-axSpA. On the contrary, patients with lo-axSpA had more peripheral arthritis (36% vs 28%) than patients with eo-axSpA. The multivariable analysis was consistent with these findings (Table 2). Patients positive for HLA-B27 (OR 0.6, 95%: 0.4-0.7), family history of SpA (OR 0.6, 95%: 0.4-0.9), IBP (OR 0.5, 95%: 0.4-0.8), AAU (OR 0.6, 95%: 0.4-0.9) and without peripheral arthritis (OR 1.5, 95%: 1.1-1.9) were less likely to have lo-axSpA. Conclusion: This study shows that axSpA indeed starts before 45 years of age in the vast majority of the patients. Even though recall bias cannot be entirely ruled out, clinicians should however be aware that late-onset disease, though infrequent, may in some cases exist. This minority phenotype has a weaker association with HLA-B27, a lower probability of family history, IBP and uveitis but more peripheral involvement. REFERENCES: 1 Rudwaleit M, et al. Ann Rheum Dis. 2009. 2 Olivieri I, et al. Clin Exp Rheumatol. 2009. Table 1. Comparison of patients and disease characteristics between patients with late and early onset axSpA Table 2. Association between patient and disease characteristics with late onset axial SpA (multivariable analysis) Acknowledgements: NIL. Disclosure of Interests: Margarida Lucas Rocha: None declared, Rita Pinheiro Torres: None declared, Sofia Ramiro AbbVie (Consultant, Grant/Research Support); Eli Lilly (Consultant); MSD (Consultant, Grant/Research Support); Novartis (Consultant, Grant/Research Support); Pfizer (Consultant, Grant/Research Support); Sanofi (Consultant); UCB Pharma (Consultant, Grant/Research Support), AbbVie (Consultant, Grant/Research Support); Galapagos (Grant/Research Support); MSD (Consultant, Grant/Research Support); Novartis (Consultant, Grant/Research Support); Pfizer (Consultant, Grant/Research Support); UCB Pharma (Consultant, Grant/Research Support), Alice Castro: None declared, Alice Neves: None declared, Ana Martins: None declared, Ana Teodósio Chícharo: None declared, Beatriz Mendes: None declared, Carolina Ochôa Matos: None declared, Catarina Dantas Soares: None declared, Claudia Miguel: None declared, Cláudia Pinto Oliveira: None declared, Hugo Parente: None declared, José Melo Gomes: None declared, Mariana Luis: None declared, Mariana Emília Santos: None declared, Maura Couto: None declared, Miguel Bernardes: None declared, Paula Valente: None declared, Roberto Pereira da Costa: None declared, Sandra Sousa: None declared, Jaime C. Branco: None declared, Fernando Pimentel-Santos: None declared, Alexandre Sepriano: None declared.