1407: Trends in Diagnostic Timing and Clinical Features of Axial Spondyloarthritis by Sex and Clinical Subtype: A Multicenter Cohort Over Seven Decades

Background/Purpose: Axial Spondyloarthritis (axSpA) frequently eludes early recognition, particularly before structural sacroiliitis becomes visible. We analyzed decade-specific diagnosis delay, clinical subtype distribution, and first-symptom profiles in men and women within a nationwide cohort to assess the impact of updating classification criteria on presentation patterns.

Methods: This was a cross-sectional data analysis from the Brazilian Spondyloarthritis Registry (RBE), including 19 centers nationwide. All patients included were diagnosed with axSpA by a rheumatologist and met the ASAS classification criteria for axSpA. Patients were grouped by the decade in which their first SpA-related symptom.

Results: A total of 791 patients were included, whose disease onset (initial symptoms) occurred between 1961 and 2024. A male predominance was observed (n = 547, 69.2%). Notably, all patients with disease onset before 1970 were male, but female representation increased progressively according to the decade of disease onset (30% in the 1970s to 50% in the 2020s). The mean diagnosis delay interval dropped from 41.7 ± 4.2 years in the 1960s (n=3) to 1.9 ± 1.5 years in 2020–2024 (n=18) (Figure 1). Diagnostic delay decreased similarly in both sexes across decades (p for interaction = 0.971). In each decade of initial symptom, delay was comparable between men and women, with no significant differences observed (all p > 0.05) (Figure 2). Radiographic axSpA (r-axSpA) accounted for all cases before 2009 and declined to 83.3 % by 2020–2024 as non-radiographic axSpA (nr-axSpA) reached 16.7 %. Diagnosis delay improved markedly for both subtypes (p< 0,001). Low back pain was the dominant initial symptom over the decades varying from 90.0% to 81.1%. Regarding symptoms, men reported more hip pain than women (23.2% vs. 8,6%, p< 0.001). Initial symptoms with upper-limb arthritis, dactylitis, cervical pain, buttock pain was similar between men and women (p >0.05). Compared to radiographic disease, non-radiographic axSpA showed more hip pain as initial symptom (23.2% vs. 8.2%, p=0.024), while frequencies of upper-limb arthritis, lower-limb arthritis, and back pain were similar (p >0.05).

Conclusion: These findings suggest a significant improvement in the recognition of axSpA in recent decades, possibly related to the adoption of new axSpA biomarkers, such as the use of magnetic resonance imaging, as well as increased awareness of the disease. This progress has led to greater recognition of previously underdiagnosed female patients. The growing proportion of non-radiographic axSpA highlights the need for early imaging-based referral protocols and management strategies.