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 Nagoya university hospital between January 2004 and May 2023. Initial symptoms considered were 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) and 19.6 (+/- 9.6) years, respectively. The back was the most common site of initial symptoms (7 patients; 41.2%), followed by the hip (5 patients; 29.4%) and knees (5 patients; 29.4%). Initial symptoms were limited to extra-axial joints and axial joints in 9 (52.9%) and 7 (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 frequently were the back, hip, and knees, with 52.9% of patients having initial symptoms limited to extra-axial joints. More than half of the patients recognised musculoskeletal diseases other than AS.