Bipolar disorder associated with rheumatoid arthritis: A case-control study

Background Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with systemic comorbidities. Recent data suggests that patients with RA have increased prevalence of the bipolar disorder. The current study investigates the association between RA and bipolar disorder. Methods A case-control study was conducted as Patients with RA were compared with age- and gender-matched controls regarding the prevalence of bipolar disorder. Pearson χ² test was used for univariate analysis and a logistic regression model was used for multivariate analysis. The study was performed utilizing the medical database of Clalit Health Services. Results The study included 11,782 patients with RA and 57,973 age- and gender-matched controls. The prevalence of Bipolar disorder in patients with RA was increased compared with the prevalence in controls (0.6% and 0.4% respectively, p=0.036). However, in a multivariate analysis the association between RA and Bipolar disorder was not significant, whereas smoking is positively correlated with Bipolar disorder (p<0.001). Conclusions By univariate analysis our data implied that patients with RA have a greater prevalence of bipolar disorder than matched controls. However, our analysis suggests that this association may have been confounded by smoking status. Further research is warranted before making inferences about this association in the level of clinical practice.