Comparison of ankylosing spondylitis and non-radiographic axial spondyloarthritis in a multi-ethnic Asian population of Singapore.

OBJECTIVES: To compare clinical characteristics, disease activity, patient-reported outcomes and associated comorbidities between patients with ankylosing spondylitis (AS) and non-radiographic axial spondyloarthitis (nr-axSpA) in a multi-ethnic Asian population of Singapore.

METHODS: We used data from the PREcision medicine in SPONdyloarthritis for Better Outcomes and Disease Remission (PRESPOND) registry in Singapore General Hospital. All patients fulfilled 2009 Assessment in AS International Working Group classification criteria for axial SpA (axSpA). Of these, all AS patients fulfilled the 1984 modified New York criteria. Baseline characteristics, medications, disease activity, patient-reported outcomes and inflammatory markers were recorded using standardized questionnaires.

RESULTS: Two hundred and sixty-two axSpA patients (82% Chinese, 79% male) were included. Mean age (SD) at diagnosis was 32.4 (13.1) years, which was similar between AS and nr-axSpA patients. AS patients were older (mean age 42.7 [13.5] vs 37.4 [13.8] years, P = 0.02), had longer disease duration (mean disease duration 10.9 [8.7] vs 6.4 [4.8] years, P < 0.01), higher Bath Ankylosing Spondylitis Metrology Index (BASMI) (mean BASMI 3.1 [2.3] vs 1.5 [1.5], P < 0.01), more frequently human leukocyte antigen (HLA)-B27 positive (82% vs 68%, P = 0.03), associated with uveitis (33% vs 17%, P = 0.03), and hypertensive (17% vs 0%, P < 0.01) compared to nr-axSpA, respectively. Nr-axSpA patients had higher Bath Ankylosing Spondylitis Global Score (BAS-G) (mean BAS-G 46.9 [16.8] vs 38.6 [20.6], P < 0.01), Bath Ankylosing Spondylitis Disease Activity Index (mean [SD] 4.2 [1.6] vs 3.5 [1.9], P = 0.02) and AS quality of life (ASQoL) (mean ASQoL 4.9 [4.8] vs 3.5 [4.1], P = 0.04) scores compared to AS patients respectively at baseline. Patient global assessment, Bath Ankylosing Spondylitis Functional Index, AS Disease Activity Score - C-reactive protein (CRP), Health Assessment Questionnaire, Short-Form 36 physical component summary and mental component summary were similar in both groups at baseline, as were medications used and mean erythrocyte sedimentation rate and CRP.

CONCLUSIONS: In our multi-ethnic Asian cohort, patients with AS are more likely to be HLA-B27 positive, have uveitis, hypertensive, and have poorer spinal mobility, while nr-axSpA patients tend to experience poorer well-being and quality of life.