Incidence of ankylosing spondylitis and spondyloarthritis in 2000-2013: a nationwide Danish cohort study

• Published in: Scandinavian journal of rheumatology Vol. 49; no. 1; pp. 21 - 27
• Main Authors: Nygaard, A, Ljungdalh, PS, Iachina, M, Nikolov, TN, Schiøttz-Christensen, B
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 02.01.2020
• Subjects: Adolescent; Adult; Denmark - epidemiology; Female; Follow-Up Studies; Humans; Incidence; Magnetic Resonance Imaging; Male; Middle Aged; Population Surveillance - methods; Registries; Retrospective Studies; Spondylarthritis - diagnosis; Spondylarthritis - epidemiology; Spondylitis, Ankylosing - diagnosis; Spondylitis, Ankylosing - epidemiology; Young Adult; Denmark
• ISSN: 0300-9742; 1502-7732
• DOI: 10.1080/03009742.2019.1616324

Objective: To describe the incidence of ankylosing spondylitis (AS) and spondyloarthritis (SpA) in the Danish population in 2000-2013, at national and regional level, and to investigate any trends in incidence over time. Methods: From the Danish National Patient Registry (NPR), we identified patients diagnosed with AS (International Classification of Diseases, 10th revision: M45) or SpA (M46) from 1 January 2000 to 31 December 2013. Patients without a relevant contact in NPR at 12-24 months after initial diagnosis were excluded. Incidence rate ratios (IRRs) were calculated using the background population of men and women aged 18-45 years in 2000-2013 as a comparator. Variations in incidence between periods and the five Danish regions were evaluated. Results: In total, 3042 incident cases were identified (AS: 1849; SpA: 1193). AS incidence increased from 476 in 2000-2004 to 660 in 2010-2013; the IRR (95% confidence interval) increased from 1.49 (1.33-1.67) in 2005-2009 to 1.74 (1.53-1.97) in 2010-2013. SpA incidence increased from 156 in 2000-2004 to 707 in 2010-2013; the IRR increased from 2.45 (2.03-2.94) in 2005-2009 to 6.31 (5.27-7.55) in 2010-2013. The incidence of both AS and SpA increased in all five regions. Conclusion: The incidence of both AS and SpA in Denmark increased from 2000 to 2013. However, the proportion of patients diagnosed with SpA rather than AS was significantly higher in 2010-2013. This may be due to increased awareness of SpA and new treatment options, but possibly also misclassification of patients with SpA.