Page 45 - Recognizing axial spondyloarthritis - Janneke de Winter

The mean symptom duration varied from 1.2±0.6 years in AS and 1.0±0.7 year in nr-axSpA (Esperanza) to 17.7±12.3 years in AS and 12.1±8.5 years in nr-axSpA (Wallis). Pooled analysis showed a male prevalence of 70.4% (CI 64.4-76.0%) in AS and 46.8% (CI 41.7-51.9%) in nr-axSpA , resulting in a pooled prevalence difference of 23.2% (CI 15.3-31.1%). When we compared male prevalence among HLA-B27+ and HLA-B27- patients in AS and nr-axSpA, this prevalence difference was maintained (24,2% more males in HLA-B27+ AS patients (CI 15.1-32.9%) and 22.3% more males in HLA-B27- AS patients (CI 14.4-30.0%)). Pooled HLA-B27 prevalence was not different in AS vs. nr-axSpA; (78.0% (CI 73.9-81.9%) in AS vs. 77.4% (CI 68.9-84.9%) in nr-axSpA).
All eight studies collected information about peripheral and extra-articular disease manifestations at baseline. Three out of eight studies (GESPIC, Kiltz and SPACE) reported patients who currently had, or had ever had, peripheral and extra-articular manifestations. Three studies only reported disease manifestations that had ever occurred (SCQM, Wallis and ESPAC) and 2 cohort studies reported only current disease manifestations (DESIR, Esperanza).
Risk of bias
All published studies (seven out of eight) were published in journals with an impact factor ˃ 3.5. The risk of bias summary for all studies is shown in supplementary Table 2. In short, the risk of bias of all studies was considered sufficiently low to be included in this meta-analysis. General bias (role of funding, reporting on ethical approval, conflict of interest) was considered low in all 8 studies. Internal validity was considered high in 3 out of 8 studies (Esperanza, SCQM and SPACE) and intermediate in 5 out of 8 studies. Source of measure of prevalence of peripheral or extra-articular disease manifestations was reported in two of the 8 studies (SCQM and SPACE). External validity was considered high in 5 out of 8 studies (Esperanza, Kiltz, SCQM, SPACE and DESIR), intermediate in one out of eight (ESPAC) and low in two out of eight studies (GESPIC and Wallis).
Heterogeneity
When comparing all study characteristics as summarized in Table 1, all eight studies were homogeneous enough to include in the meta-analysis. Statistical heterogeneity was measured for each of the peripheral or extra-articular disease manifestations.
Meta-analysis
Peripheral arthritis
Pooled analysis showed a current peripheral arthritis prevalence of 22.9% (CI 5.7- 46.0%) in AS and 25.2% (CI 8.9-45.7%) in nr-axSpA , resulting in a pooled prevalence difference of 0.7% (CI -5.4-6.7%) favoring AS. Quantitative heterogeneity was not statistically significant and the level of inconsistency was moderate (Chi2 = 7.29, P=0.12, Tau2 = 0.00, I2 = 45%). The pooled prevalence of a history of peripheral
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