Objective: The aim of our study was to compare the clinical, functional, and radiographic outcomes at different ages of onset in patients with ankylosing spondylitis (AS). Methods: A total of 546 patients were enrolled consecutively and classified into 3 groups based on their age at symptom onset: (1) juvenile-onset AS (age ≤ 16 years; JoAS); (2) adult-onset AS (> 16 but <40 years; AoAS); and (3) late-onset AS (≥ 40 years; LoAS). We compared the differences among the 3 groups. OR for disease outcomes were calculated and adjusted for sex, HLA-B27, and disease duration. Results: There were 67 patients (12.3%) with JoAS, 460 (84.2%) with AoAS, and 19 (3.5%) with LoAS. Male sex and HLA-B27 were associated with a younger age at onset (p <0.001). Compared to patients with AoAS, patients with JoAS were more likely to present with peripheral arthritis, while patients with JoAS and LoAS were less likely to have back pain at the onset of AS (p <0.05). After controlling for multiple covariates, JoAS was found to be associated with a worse functional outcome and global assessment, and a high serum immunoglobulin A level (p <0.05). Patients with JoAS had less lumbar spinal radiographic severity (p <0.05). There were no statistical differences in clinical or functional outcome between the LoAS and AoAS groups. None of the LoAS patients had radiographic hip involvement. Conclusion: Sex and HLA-B27 are significantly associated with age at onset of AS. Both JoAS and LoAS have their distinctive symptoms/signs at onset and different disease outcomes.
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