Clinical characteristics of Japanese patients with axial spondyloarthritis, and short-term efficacy of adalimumab.

Background: Ankylosing spondylitis (AS) is rarer in Japan than in Europe, probably because the European criteria, not well known by Japanese general physicians, regard AS as a progressive stage of axial spondyloarthritis (SpA). HLA-B27 is an important diagnostic marker of SpA; however, the incidence of the HLA-B27 allele is as low as 0.4 % in Japan.