Patients with rheumatoid arthritis have a higher risk of bipolar disorder: A systematic review and meta-analysis

The current study was conducted with the aim to investigate the relationship between rheumatoid arthritis (RA) and bipolar disorder (BD). Potentially eligible studies were identified from Medline and EMBASE databases from inception to May 2019. Eligible cohort studies must include patients with RA and comparators without RA, follow them for incident BD and report the relative risk, hazard risk ratio or standardized incidence ratio and associated 95% confidence intervals (CI) comparing the incidence of BD between the two groups. Eligible case-control studies must include cases with BD and controls without BD, explore prior history of RA and report the odds ratio and associated 95% CI for this association. Point estimates with standard errors were extracted from individual study and were combined together using random-effect model, generic inverse variance method. A total of six studies fulfilled the inclusion criteria and were included into the meta-analysis. The risk of developing BD was significantly higher among patients with RA than individuals without RA with the pooled relative risk of 2.06 (95% CI, 1.34-3.17; I² 86%). Chronic inflammation is a potential mechanism and could be a modifiable risk factor of BD. However, further studies are still required to confirm this.