Bipolar disorder and comorbidity: increased prevalence and increased relevance of comorbidity for hospital-based mortality during a 12.5-year observation period in general hospital admissions.

Background: Bipolar disorder (BD) is associated with an increase of psychiatric and physical comorbidities, but the effects of these disorders on general hospital-based mortality are unclear. Consequently, we investigated whether the burden of comorbidity and its relevance on hospital-based mortality differed between individuals with and without BD during a 12.5-year observation period in general hospital admissions.

Methods: During 1 January 2000 and 30 June 2012, 621 individuals with BD were admitted to three General Manchester Hospitals. All comorbidities with a prevalence ≥1% were compared with those of 6210 randomly selected and group-matched hospital controls of the same age and gender, regardless of priority of diagnoses. Comorbidities that increased the risk for hospital-based mortality (but not mortality outside of the hospitals) were identified using multivariate logistic regression analyses.

Results: Individuals with BD had a more severe course of disease than controls that was associated with a higher total number of in-hospital deaths. Individuals with BD compared to controls had a substantial higher burden of comorbidities, the most frequent comorbidities included asthma, type-2 diabetes mellitus (T2DM), and alcohol dependence. 18 other diseases with a surplus of diabetes related complications were also increased. Fourteen comorbidities contributed to the prediction of hospital-based mortality in univariate analyses. Risk factors for hospital-based mortality in multivariate analyses were ischemic stroke, pneumonia, bronchitis, chronic obstructive pulmonary disease, T2DM, and hypertension. The impact of T2DM on hospital-based mortality was higher in individuals with BD than in controls.

Limitations: The study design was not assigned to assess the type of BD, the current bipolar status, and if individuals with BD were treated with medication. It was neither possible to compare drug effects, nor to compare the adherence to treatment between samples.

Conclusion: In one of the largest samples of individuals with BD in general hospitals, the excess comorbity in individuals with BD compared to controls is in particular caused by asthma and T2DM. T2DM and its complications cause significant excess hospital-based mortality in individuals with BD.