Epidemiology of Spondyloarthritis

Spondyloarthritis (SpA) represents a group of interrelated diseases with common clinical features and a close association with HLA-B27. Figures on the incidence and prevalence of diseases vary highly dependent on methodological differences between studies, the case definition used to classify disease and on the prevalence of HLA-B27 in the population studied. When summarizing the available literature, incidence rates of SpA are mainly based on the ESSG criteria and range between 0.48 and 63/100.000 while prevalence rates vary between 0.01 and 2.5%. For ankylosing spondylitis (AS), the most widely recognized representative of the SpA group of diseases, incidence rates of 0.44-7.3/100.000 and prevalence rates of 0.007-1.7% have been described in studies that were based on the (modified) New York criteria to classify cases. The incidence of psoriatic arthritis (PsA) varied from 3.6 up to 23.1/100.000 in different studies and prevalence between <0.1% and 0.4%, using a variety of classification criteria. The incidence of ReA has been estimated between 0.6 up to 28/100.000 in studies based on different source populations and different case definitions. The newly proposed criteria for axial SpA and peripheral SpA present an attractive new approach to facilitate classification of the SpA into two main subtypes and the axial SpA criteria allow earlier detection of patents with inflammatory back pain. It should be emphasized that these criteria were developed for use in a (specialized) clinical setting and not for large epidemiological studies