The condition of symmetrical sacroiliitis in axial spondyloarthritis: Comment on the article by Coates et al

To the Editor:I read the article by Coates et al (1), recently published in Arthritis Care & Research, with great interest as it relates to the radiographic phenotype of axial spondyloarthritis according to the presence of HLA– B27, regardless of the primary diagno-sis of ankylosing spondylitis (AS) or psoriatic arthritis (PsA). The authors stated that the HLA– B27 gene is related to radiographic progression, syndesmophyte symmetry, and marginal syndes-mophytes, but not to sacroiliac symmetry. I would like to offer some suggestions from a biomechanical aspect, based on their important findings. Chronic biomechanical stress and microdam-age have been postulated as major triggering factors for lesion development, particularly in PsA. As compatible with a biome-chanical standpoint, tissue- specific kinetic factors (applied forces during motion) may play a critical role in the development of psori-atic lesions. Thus, PsA can de defined as an inflammatory disorder of more mobile musculoskeletal structures when AS is considered.