Update on the epidemiology, risk factors, and disease outcomes of axial spondyloarthritis.

Axial spondyloarthritis (axSpA) is the prototype of a class of a rheumatic chronic inflammatory disease named spondyloarthritis (SpA). The prevalence of axSpA ranges between 0.1% and 1.4% globally, hence showing geographic differences that can be explained mostly by the prevalence of the HLA-B27 antigen. However, not many studies have evaluated the incidence of this disease. Inflammation may be initiated in the enthesis as a consequence of the action of IL-23, which can activate resident T cells. The elevated expression of IL-23 has been explained by three hypotheses: the presence of HLA-B27, variations in the gut microbiome and the biomechanical stress at the enthesis. However, the role of IL-23 in this whole context is still unclear. In axSpA, the presence of syndesmophytes at baseline, systemic inflammation, and smoking may promote the spinal radiographic damage in these patients. The most frequent comorbidity in these patients is osteoporosis, which is directly associated with ankylosis and inflammation.