Clinical characteristics of nonradiographic axial spondyloarthritis in Korea: a comparison with ankylosing spondylitis

Aim To evaluate the clinical characteristics and outcomes of nonradiographic axial spondyloarthritis (nr‐axSpA) in Korean patients. Methods A retrospective analysis evaluated 155 patients with nr‐axSpA at a single tertiary hospital between January 2001 and January 2011. Baseline characteristics and clinical courses were reviewed and compared with those of patients with ankylosing spondylitis ( AS ). Results The mean age at disease onset was 29.5 ± 10.8 years and 52 (33.5%) patients were female. The mean age at symptom onset was older (29.5 ± 10.8 vs 25.9 ± 9.2, respectively, P  < 0.001) and the male‐to‐female ratio was lower (2 : 1 vs 5 : 1, respectively, P  = 0.001) in patients with nr‐axSpA compared with patients with AS . The proportion of females was higher among patients with late onset SpA than early‐onset nr‐axSpA (55.0% vs 30.1%, respectively, P  = 0.029). Among 74 patients with nr‐axSpA, whose follow‐up duration was more than 1.5 years, 29 (39.2%) patients progressed to AS during the follow‐up period. The proportion of females was lower in progressors that that of non‐progressors (13.8% vs 44.4%, respectively, P  = 0.010). Presence of syndesmophyte and minimal X‐ray changes at baseline were frequently observed in progressors compared with non‐progressors (26.7% vs 0.0%, P  = 0.006 and 69.0 vs 35.6%, P  = 0.005, respectively). Conclusions The predominance of male patients is more prominent among Korean patients with SpA compared with Caucasians. Female nr‐axSpA patients had late symptom onset and less progression to AS . X‐ray changes at baseline were associated with radiographic progression.