Page 51 - Recognizing axial spondyloarthritis - Janneke de Winter
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continuum regardless of the presence and extent of radiographic changes (11– 13). Two important conclusions can be drawn from this meta-analysis. First, peripheral and extra-articular disease manifestations significantly contribute to the burden of disease in axial SpA. These results are in contrast with the relatively limited contribution of peripheral and extra-articular disease to disease monitoring and outcome measurement of axial SpA. Second, these results show that differentiating between AS and nr-axSpA is artificial and should therefore be avoided, especially when selecting patient populations for research and treatment populations. These patients can best be combined into one group of axial SpA.
Uveitis is less prevalent in nr-axSpA than in AS (with a pooled prevalence difference of 6.2%). This prevalence difference was not explained by a difference in HLA-B27 prevalence between nr-axSpA and AS, since HLA-B27 prevalence did not differ between both groups. Zeboulon and colleagues showed that uveitis prevalence was higher in HLA-B27+ patients (29), although this was not confirmed in the meta-analysis on extra-articular manifestations in AS of Stolwijk et al (30). The higher uveitis prevalence in AS in this meta-analysis might be explained by the longer mean disease duration in AS (presuming that uveitis in axial spondyloarthritis does not necessarily occur at the start of the disease and thus needs time to develop). This hypothesis is supported by 1) the fact that the included cohort studies with longer mean disease duration generally showed a higher ‘history of uveitis’ prevalence (Kiltz, SCQM, Wallis): excluding those cohort studies from the meta-analysis resulted in a non-significant uveitis prevalence difference between AS and nr-axSpA (data not shown) and 2) the fact that the prevalence of ‘current uveitis’ did not differ between AS and nr-axSpA.
To our knowledge, this is the first meta-analysis systematically comparing AS with nr-axSpA. Strengths of the current study are the systematic approach in which we have chosen to include only studies that were designed to compare both disease entities, preferably in a prospective manner. Importantly, we have excluded clinical trials that included patients that were selected because of a higher activity and/or severity of their disease (which would have led to channeling bias).
This study has several limitations. First, summarizing the prevalence of peripheral and extra-articular disease manifestations was not the main objective of most of the primary studies included. This might influence the accuracy of reporting these disease manifestations (potential detection bias). Most studies did not report on how the different disease manifestations were measured. We should take into account that the prevalence of some of the disease manifestations, which had ‘ever’ occurred, were mainly obtained by collecting historic patient-reported information (recollection bias). However, the between-study inconsistency of most of the disease manifestations was only moderate (arthritis, enthesitis and dactylitis) or even low (uveitis, psoriasis, IBD), suggesting a significant level of agreement. Second, selection bias is another possible weakness of this meta- analysis and, more importantly, of the included primary studies. We hopefully limited the magnitude of selection bias in this meta-analysis by a thoroughly
DISEASE MANIFESTATIONS IN AXIAL SPA
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