Epidemiology of spondyloarthritis in North America.

Many challenges have made it difficult to determine the prevalence of spondyloarthritis (SpA) in North America. They include the ethnic heterogeneity of the population, the lack of feasibility of applying current criteria (such as requirements for human leukocyte antigen-B27 testing and imaging studies such as pelvic radiographs and magnetic resonance imaging scanning) and the transient nature of some SpA symptoms (ie, peripheral arthritis and enthesitis). Current estimates of the prevalence of SpA in the United States range between 0.2% and 0.5% for ankylosing spondylitis, 0.1% for psoriatic arthritis, 0.065% for enteropathic peripheral arthritis, between 0.05% and 0.25% for enteropathic axial arthritis and an overall prevalence of SpA as high as >1%. With newer population-based instruments becoming available, the availability of the widely validated European Spondyloarthropathy Study Group criteria and the lower cost and greater feasibility of genetic testing, opportunities for true population-based studies of SpA are possible and will likely soon ensue.