SAT0682 “incidence and regional variation of ankylosing spondylitis and spondyloarthritis 2000–2013: a nationwide cohort study”
Authors: A. Nygaard, P.M. Ljungdalh, M. Iachina, B. Schiøttz-Christensen
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Spondyloarthritis is a group of inflammatory rheumatic diseases with Ankylosing Spondylitis (AS) as the major subgroup. Only a few studies worldwide have reported incidences of AS and their trend over time. <h3>Objectives</h3> To describe the incidences of Ankylosing Spondylitis (AS) and spondyloarthritis (SpA) in the Danish population in 2000–2013, at both national and regional level. To establish if there is a trend in incident cases over time and test if such a trend may be explained by use of MRI scans for diagnostic evaluation. <h3>Methods</h3> In the Danish National Patient Registry, we identified all patients with a valid Danish civil registration number who received an AS (ICD10:DM45) or SpA (ICD10:DM46) diagnosis during the time period from 1 January 2000 until 31 December 2013. Incident cases were identified and incidence rates described as rates per 1/100.000 of AS and SpA were calculated for each year. Variation among the five Danish regions were evaluated and correlated to the diagnostic use of MRI. <h3>Results</h3> We identified 3620 incident cases (AS: 2116, SpA: 1504). Males are overrepresented among AS incidents (58%–80%), both nationwide and regionally. The percentages of males with an AS diagnosis are stable throughout the time period (65%–69%). Females are overrepresented among SpA incidents nationwide and in most regions. In the Region of Southern Denmark, there is a small overrepresentation of males for both SpA and AS diagnoses (58%). The number of nationwide AS incident cases increases between 2005 and 2009 from 534 (rate: 0.52) to 828 cases (0.82). During 2010–2013 the AS incidence decreased to 754 (0.94). The number of SpA incident cases increased from 220 (0.21) in 2009 to 430 (0.43) in 2009 with an additional increase in incidence to 854 (1.06) in 2010–2013. The trend is the same throughout the five regions. MRI was used for diagnostic purposes in only 10%–15% of the patients in 2002. In 2013 the number had increased to 95.0% of male patients and 94.3% of female patients diagnosed with AS and 98.5/98.1% of patients diagnosed with SpA. <h3>Conclusions</h3> In this Danish nationwide cohort, the incidence of AS increased during the years 2000–2004 and stabilised in 2005–2013 which is in line with previous studies exploring the trends of AS incidence. The SpA incidence increased significantly during the years 2000 to 2013. This might be caused by the implementation of the ASA criteria in 2009, which included the "imaging arm", and by increased access to MRI for diagnostic evaluation in patients with low back pain. This might lead to overestimation and/or misdiagnosis of SpA because signs of inflammatory changes in the sacroiliac joint are a common finding in MRIs of low back pain patients. <h3>References</h3> [1] Carbone L., Cooper C, et al. Ankylosing spondylitis in Rochester, Minnesota, 1935–1989. Is the epidemiology changing. Arthritis Rheum1992Dec;35(12):1476–82. [2] Wright A., Cynthia S, et al. Time Trends in Incidence, Clinical Features, and Cardiovascular Disease in Ankylosing Spondylitis. Arthritis Care &amp; Research2015June;67(6):836–841DOI: 10.1002/acr.22512 [3] Carter E, et al. Epidemiology of ankyosing spondylitis in Rochester, 1935–1973. Arthritis and Rheumatism1979April;22(4). [4] Braun J, Sieper J. Ankylosing spondylitis. Lancet2007Apr 21;369(9570):1379–90. <h3>Disclosure of Interest</h3> None declared