Clinical features of juvenile onset ankylosing spondylitis in Japanese patients.

Objectives: This retrospective study aimed to examine the clinical features of juvenile onset ankylosing spondylitis (JoAS) in Japanese patients.

Methods: We examined clinical symptoms (including initial symptoms) and the progression to diagnosis of AS in 17 Japanese JoAS patients at our institute between January 2004 and May 2023. Initial symptoms were considered pain at axial joints and/or extra-axial joints.

Results: Mean ages (± standard deviation) at onset and diagnosis of AS were 12.9 (± 2.0) years and 19.6 (± 9.6) years, respectively. The back was the most common site of initial symptoms (seven patients; 41.2%), followed by the hip (five patients; 29.4%) and knees (five patients; 29.4%). Initial symptoms were limited to extra-axial joints and axial joints in nine (52.9%) and seven (41.2%) patients, respectively. Nine patients (52.9%) were recognised as a musculoskeletal disease other than AS, such as oligoarticular juvenile idiopathic arthritis.

Conclusions: Sites of initial symptoms were frequently the back, hip, and knees, with 52.9% of patients having initial symptoms limited to extra-axial joints. More than half of the patients were recognised musculoskeletal diseases other than AS.