The spondyloarthropathies (SpA) include 7 interrelated rheumatic disorders that are characterized by the presence of both synovitis and enthesitis. A common genetic feature is a correlation with the human lymphocyte antigen (HLA)-B27 genotype. Other accompanying characteristics can include family history, psoriasis, manifestations in the gut or other organ systems, alternating buttock pain, or sacroiliitis. The prevalence of SpA resembles that of rheumatoid arthritis and affects approximately 0.6 to 1.9% of the population. The prototypical disease of this group is ankylosing spondylitis (AS) which has a prevalence estimated to be as high as 1.4%. The HLA-B27 gene is present in >90% of AS patients. References Braun J et al Curr Opin Rheumatol 2003;15:394-407. Gran J et al 1997;36:766-71. Khan M Ann Int Med 2002;136:896-907.
Radiological progression is much slower in AS compared with RA and changes in structural damage may not be evident for 2 years.