Clinical characteristics of non-radiographic axial spondyloarthritis: Results of the Korean Nonradiographic Axial SPondyloArthritis (KONASPA) data.

AIM To evaluate clinical characteristics and natural history of non-radiographic axial spondyloarthritis (nr-axSpA) using KOrean Nonradiographic Axial SPondyloArthritis (KONASPA) data. METHODS Data were collected from 11 centers in South Korea. A total of 278 patients with nr-axSpA from January 2018 to July 2020 were included. Demographic data, clinical features, comorbidities, disease activity, medications, and laboratory results were collected. RESULTS Mean age at symptom onset was 28.2 ± 14.2 years. Of 278 patients, 152 (54.7%) were male. Mean Bath Ankylosing Spondylitis Disease Activity Index at diagnosis was 3.5 ± 2.1. Dyslipidemia was the most common comorbidity (8.4%), followed by hypertension (6.1%). Mean age at diagnosis of nr-axSpA was older in female patients than in male patients (31.8 ± 15.8 years vs 24.9 ± 12.0 years, P < 0.001). Enthesitis and uveitis were more frequently found in female patients than in male patients. Thirty-one (11.1%) participants with nr-axSpA progressed to ankylosing spondylitis. The median follow-up duration was 48 months. In multivariable Cox regression analysis, age at symptom onset (hazard ratio [HR] 0.93, 95% confidence interval (CI) 0.88-0.97, P = 0.006), body mass index (BMI) (HR 1.24, 95% CI 1.06-1.44, P = 0.005) and sacroiliitis grade (HR 1.86, 95% CI 1.19-2.92, P = 0.006) were associated with progression to ankylosing spondylitis. CONCLUSIONS Results of nationwide data revealed that women with nr-axSpA showed a late disease onset and more extra-articular manifestations than men. Young age at symptom onset, high BMI, and presence of radiographic sacroiliitis at diagnosis were risk factors for progression to AS.