A Nationwide Questionnaire Survey on the Prevalence of Ankylosing Spondylitis and Non-Radiographic Axial Spondyloarthritis in Japan.

Objective This nationwide study aimed to reveal the prevalence of ankylosing spondylitis (AS) and non-radiographic axial spondyloarthritis (nr-ax SpA), and the positive rate of human leukocyte antigen (HLA) among these patients in Japan. Methods The first survey was conducted in 2221 randomly selected facilities (26.3%) in September, 2018, where the patients with AS/nr-ax SpA were taken care of from January to December, 2017. We estimated the total number of these patients using response and extraction rate. A second survey was conducted in 117 facilities (49.8%) to assess for HLA-B 27 positivity rate and clinical features. Results The estimated total number of the patients with AS and nr-ax SpA were 3200 (95% confidence interval [CI]: 2400-3900) and 800 (530-1100), suggesting that the prevalence of AS and nr-ax SpA in general population were 2.6/100,000 (0.0026%) and 0.6/100,000 (0.0006%), respectively. Although 55.5 % (76/137) of patients with AS were HLA-B27 positive, those whose age of onset was estimated to be over 50 years tended to undergo less HLA-B27 testing. Conclusion This study revealed the lower prevalence of AS/nr-ax SpA in Japan, compared to those in other countries. Further studies are required to reveal the association of HLA-B27 with the clinical features.