Is the association of alcohol use disorders with major depressive disorder a consequence of undiagnosed bipolar-II disorder?

Background There is emerging evidence that there is a spectrum of expression of bipolar disorder. This paper uses the well-established patterns of comorbidity of mood and alcohol use disorder to test the hypothesis that application of an expanded concept of bipolar-II (BP-II) disorder might largely explain the association of alcohol use disorders (AUD) with major depressive disorder (MDD). Method Data from the Zurich study, a community cohort assessed over 6 waves from ages 20/21 to 40/41, were used to investigate the comorbidity between mood disorders and AUD. Systematic diagnostic criteria were used for alcohol abuse, alcohol dependence, MDD, and BP-II. In addition to DSM criteria, two increasingly broad definitions of BP-II were employed. Results There was substantially greater comorbidity for the BP-II compared to major depression and for alcohol dependence compared to alcohol abuse. The broadest concept of BP-II explained two thirds of all cases of comorbidity of AUD with major depressive episodes (MDE). In fact, the broader the definition of BP-II applied, the smaller was the association of AUD with MDD, up to non-significance. In the majority of cases, the onset of bipolar manifestations preceded that of drinking problems by at least 5 years. Conclusions The findings that the comorbidity of mood disorders with AUD was primarily attributable to BP-II rather than MDD and that bipolar symptoms usually preceded alcohol problems may encourage new approaches to prevention and treatment of AUD.