Physical comorbidities increase the risk of psychiatric comorbidity in immune-mediated inflammatory disease.

OBJECTIVE: We tested the association between physical comorbidity and incident depression, anxiety disorder and bipolar disorder in three immune-mediated inflammatory diseases (IMID): inflammatory bowel disease (IBD), multiple sclerosis (MS) and rheumatoid arthritis (RA) versus age-, sex- and geographically-matched controls.

METHODS: Using population-based administrative data we identified 6119 persons with IBD, 3514 persons with MS, 10,206 persons with RA and 97,727 matched controls. We identified incident cases of depression, anxiety disorder and bipolar disorder in these populations. We evaluated the association of physical comorbidities with incident psychiatric comorbidity using Cox regression, adjusting for sociodemographic factors and index year.

RESULTS: The risk of incident depression, anxiety disorders and bipolar disorder was higher in each IMID cohort versus their matched cohorts. The risk of incident psychiatric comorbidity increased with an increasing number of physical comorbidities for each psychiatric comorbidity evaluated, across all IMID. Adjustment for physical comorbidity did not attenuate the increased risk of psychiatric comorbidity in the IMID cohorts versus their matched cohorts.

CONCLUSION: The increased incidence of psychiatric comorbidity in IMID versus matched general population cohorts is not accounted for by their increased prevalence of physical comorbidities. However, within IMID cohorts, physical comorbidity increases the risk of psychiatric comorbidity.