Supplementary Material for: Association between Hidradenitis Suppurativa and Inflammatory Arthritis: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> Several studies report a high prevalence of inflammatory arthritis among hidradenitis suppurativa (HS) patients. <b><i>Objectives:</i></b> To study the association between HS and inflammatory arthritis. <b><i>Methods:</i></b> The systematic review and meta-analysis were performed according to the PRISMA guidelines to identify the association between HS and inflammatory arthritis, spondyloarthritis, ankylosing spondylitis (AS), and rheumatoid arthritis (RA). <b><i>Results:</i></b> Seven studies were entered in the analysis, with 200,361 HS patients and 385,599 controls. Pooled analysis illustrated a significantly increased risk of inflammatory arthritis in HS patients compared to controls (odds ratio [OR] 3.44; 95% confidence interval [CI] 1.92–6.17). There was also a statistically significant association between HS and spondyloarthritis (OR 2.10; 95% CI 1.40–3.15), and between HS and AS (OR 1.89; 95% CI 1.14–3.12). Moreover, pooled analysis showed a statistically significant association between HS and RA (OR 1.96; 95% CI 1.28–2.98). <b><i>Conclusions:</i></b> Our findings show that HS patients have a 3-fold increased risk of developing inflammatory arthritis. HS patients are specifically at a higher risk for spondyloarthritis, its subtype AS, and RA.