Age and symptoms at onset of ankylosing spondylitis in Japanese patients

ABSTRACT 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.