Objective: To test two hypotheses of psychiatric comorbidity in bipolar disorder (BD): (i) comorbid disorders are independent of BD course, or (ii) comorbid disorders associate with mood.
Methods: In the Jorvi Bipolar Study (JoBS), 191 secondary-care outpatients and inpatients with DSM-IV bipolar I disorder (BD-I) or bipolar II disorder (BD-II) were evaluated with the Structured Clinical Interview for DSM-IV Disorders, with psychotic screen, plus symptom scales, at intake and at 6 and 18 months. Three evaluations of comorbidity were available for 144 subjects (65 BD-I, 79 BD-II; 76.6% of 188 living patients). Structural equation modeling (SEM) was used to examine correlations between mood symptoms and comorbidity. A latent change model (LCM) was used to examine intraindividual changes across time in depressive and anxiety symptoms. Current mood was modeled in terms of current illness phase, Beck Depression Inventory (BDI), Young Mania Rating Scale, and Hamilton Depression Rating Scale; comorbidity in terms of categorical DSM-IV anxiety disorder diagnosis, Beck Anxiety Inventory (BAI) score, and DSM-IV-based scales of substance use and eating disorders.
Results: In the SEM, depression and anxiety exhibited strong cross-sectional and autoregressive correlation; high levels of depression were associated with high concurrent anxiety, both persisting over time. Substance use disorders covaried with manic symptoms (r = 0.16-0.20, p < 0.05), and eating disorders with depressive symptoms (r = 0.15-0.32, p < 0.05). In the LCM, longitudinal intraindividual improvements in BDI were associated with similar BAI improvement (r = 0.42, p < 0.001).
Conclusions: Depression and anxiety covary strongly cross-sectionally and longitudinally in BD. Substance use disorders are moderately associated with manic symptoms, and eating disorders with depressive mood.