Increased incidence of psychiatric disorders in immune-mediated inflammatory disease.

<bold>Objective: </bold>Although psychiatric comorbidity is known to be more prevalent in immune-mediated inflammatory diseases (IMID) than in the general population, the incidence of psychiatric comorbidity in IMID is less understood, yet incidence is more relevant for understanding etiology.<bold>Methods: </bold>Using population-based administrative (health) data, we conducted a retrospective cohort study over the period 1989-2012 in Manitoba, Canada. We identified 19,572 incident cases of IMID including 6119 persons with inflammatory bowel disease (IBD), 3514 persons with multiple sclerosis (MS), 10,206 persons with rheumatoid arthritis (RA), and 97,727 age-, sex- and geographically-matched controls. After applying validated case definitions, we estimated the incidence of depression, anxiety disorder, bipolar disorder and schizophrenia in each of the study cohorts. Using negative binomial regression models, we tested whether the incidence rate of psychiatric comorbidity was elevated in the individual and combined IMID cohorts versus the matched cohorts, adjusting for sex, age, region of residence, socioeconomic status and year.<bold>Results: </bold>The relative incidence of depression (incidence rate ratio [IRR] 1.71; 95%CI: 1.64-1.79), anxiety (IRR 1.34; 95%CI: 1.29-1.40), bipolar disorder (IRR 1.68; 95%CI: 1.52-1.85) and schizophrenia (IRR 1.32; 95%CI: 1.03-1.69) were elevated in the IMID cohort. Depression and anxiety affected the MS population more often than the IBD and RA populations.<bold>Conclusions: </bold>Individuals with IMID, including IBD, MS and RA are at increased risk of psychiatric comorbidity. This increased risk appears non-specific as it is seen for all three IMIDs and for all psychiatric disorders studied, implying a common underlying biology for psychiatric comorbidity in those with IMID. [ABSTRACT FROM AUTHOR]