Epidemiology of axial spondyloarthritis: an update

To provide an update of the prevalence and incidence of axial spondyloarthritis in the general population and in patients with spondyloarthritis-related conditions, environmental risk factors for ankylosing spondylitis, progression from nonradiographic axial spondyloarthritis to ankylosing spondylitis, mortality, and risks for cardiovascular events in patients with ankylosing spondylitis.

Increasingly, administrative healthcare data have been used to study disease frequency and outcomes. The prevalence of ankylosing spondylitis ranged from 9 to 30 per 10 000 persons, which are lower than previous estimates. Data on whether childhood infections influence the risk of ankylosing spondylitis were equivocal, while having been breast-fed may be protective. Progression of patients with nonradiographic axial spondyloarthritis to ankylosing spondylitis is slow, with estimates of 5.1% in 5 years and 19% in 10 years. Risk of mortality is slightly increased in ankylosing spondylitis. Risks for cardiovascular events in ankylosing spondylitis were either not different from, or only slightly higher than in controls. No studies have examined these outcomes in the broader group of patients with axial spondyloarthritis.

Expanded use of administrative and registry data has facilitated studies of the epidemiology of ankylosing spondylitis, but lack of specific diagnostic codes limits use of these resources for studying axial spondyloarthritis in general.