Page 41 - Recognizing axial spondyloarthritis - Janneke de Winter

selection bias and maximize accuracy of the data. Reporting the prevalence of peripheral and extra-articular disease manifestations did not necessarily have to be the primary outcome of the study.
All patients with axSpA had to fulfill the ASAS axial SpA criteria as defined in 2009 or an equivalent if the study was conducted before 2009 (3) (a modified version of the European Spondylarthropathy Study Group (ESSG) criteria (37)) . All patients with AS had to meet the mNY-criteria for AS (38). All nr-axSpA patients had to fulfill the ASAS MRI criteria or the clinical arm of the ASAS criteria for axial SpA (4), (or an equivalent if the study was conducted before 2009).
SPondyloArthritis Caught Early (SPACE) cohort study
We added unpublished data to our meta-analysis of one prospective cohort study. The SPACE cohort was described in detail previously (23). In short, the SPACE cohort is a longitudinal cohort of patients aged 16 years and older, with chronic back pain for at least 3 months but less than 2 years, and with onset before the age of 45 years. In this meta-analysis, we added data for all patients with AS and nr- axSpA included between January 2009 and 2014 in two of the participating centers (Amsterdam UMC and the Leiden University Medical Center).
Data extraction and management
Two review authors (JdW, LvM) independently extracted data by using a predesigned form. The following details were extracted whenever available: first author, name of the study, country, year of publication, study design, study characteristics, sample size, mean age of patients, male/female ratio, mean disease duration, HLA-B27 positivity and percentage of the cohort in which HLA-B27 was measured, timing and prevalence of peripheral and extra-articular disease manifestations. Whenever data on certain peripheral or extra-articular disease manifestations were missing, we contacted the authors of the concerning article. Furthermore, we requested data on the distribution of male/females among HLA-B27+ and HLA-B27- patients with AS and nr-axSpA.
Assessment of risk of bias
Two review authors (JdW, LvM) assessed the potential risk of bias in all of the included studies by using the Methodological Evaluation of Observational research (MORE) checklist (39), which we adapted to our research question. The MORE checklist includes parameters on reporting of statement of potential conflict of interest, study funding, ethical approval, external validity (was the gold standard for the diagnosis of AS and nr-axSpA used? Was there (reporting on) sampling bias?), and internal validity (how and when was the prevalence of peripheral or extra-articular disease symptoms measured?).
Assessment of heterogeneity
First, we assessed qualitative heterogeneity across studies by comparing them
DISEASE MANIFESTATIONS IN AXIAL SPA
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