HLA B 27 Spondyloarthritides
The spondyloarthropathies (SpAs) are a group of inflammatory joint diseases that affect the axial skeleton, causing clinical syndromes characterized by chronic back pain and large joint arthritis. Ankylosing spondylitis (AS) is the commonest of the SpAs, which comprise six subtypes: ankylosing spondylitis, reactive arthritis (ReA), psoriatic arthritis (PsA), spondyloarthritis associated with inflammatory bowel disease (IBD), juvenile arthritis associated spondylitis, and undifferentiated spondyloarthritis. These diseases are associated with the HLA B27, MHC class I allotypes. SpAs are characterized clinically by asymmetrical joint involvement, predominantly involving the lower limbs, associated with enthesitis (inflammation of the tendon insertion into bone) and extra-articular manifestations including: anterior uveitis (AU), psoriasis, and inflammatory bowel disease – ulcerative colitis and Crohn’s disease. The cardiovascular system may also rarely be involved causing aortitis and cardiac conduction abnormalities. The prevalence of the SpAs is now considered to be higher than rheumatoid arthritis in the general population and the prevalence of AS is between 0.1% and 1.4%, and studies from several countries indicate an incidence of AS of between 0.5 and 14 cases per 100,000 per year.