Age and symptoms at onset of ankylosing spondylitis in Japanese patients.

OBJECTIVES: To examine the age at onset and initial symptoms as clinical features of ankylosing spondylitis in Japanese patients. METHODS: This retrospective study included 60 Japanese patients diagnosed with ankylosing spondylitis at our institute between January 2004 and June 2021. Initial symptoms were considered pain in axial joints and/or extra-axial joints. If a patient had initial symptoms at multiple sites, each site was counted. We assessed trends for the number of patients and sites of initial symptoms according to age at onset. RESULTS: Mean age (± standard deviation) at onset was 28.9 (± 14.3) years. Approximately one-third of patients experienced onset before age 20. The back was the most common site of initial symptoms (36.7%), followed by the hip (26.7%), knee (15%), buttocks (15%), neck (10%), finger (6.7%), shoulder (3.3%), and others (including overlapping sites). Thirty-two (53.3%) and 25 (41.7%) patients had initial symptoms only in axial joints and only in extra-axial joints, respectively. The proportion of patients with initial symptoms only in extra-axial joints significantly decreased with increasing age (p = .024). CONCLUSIONS: Sites of initial symptoms were frequently the back, hip, knee, and buttocks, and 41.7% had initial symptoms only in extra-axial joints. Younger onset patients frequently had extra-axial involvement.