Background: We sought to describe features that distinguish individuals with bipolar disorder from major depressive disorder.
Methods: A retrospective chart review of adult outpatients (N = 1000) seeking evaluation and treatment was conducted at the Mood Disorders Psychopharmacology Unit (MDPU), University Health Network, University of Toronto between October 2002 and November 2005 was conducted. Sociodemographic parameters, illness-characteristics and therapeutic interventions were evaluated and compared.
Results: The MDPU referring diagnosis were major depressive disorder (52%), bipolar disorder (29%), and unspecified (19%). Of all individuals with a non-bipolar entry diagnosis (n = 699), 23% (n = 159) were subsequently diagnosed with bipolar disorder (p < 0.001); the majority of whom (n = 117, 74%) received a non-bipolar I disorder diagnosis [e.g. bipolar II disorder (n = 71); bipolar NOS disorder (n = 46) (p < 0.001)]. Higher rates of unemployment/disability, previous depressive episodes, psychiatric hospitalization, comorbid hypertension, and lifetime substance use disorders, as well as an earlier age of illness-onset were more frequently endorsed by individuals with a diagnosis of bipolar disorder. Fifteen percent of individuals who were newly-diagnosed with bipolar disorder reported a history of antidepressant-associated mania.
Conclusions: The majority of individuals with a newly-diagnosed bipolar disorder at this tertiary center have a non-bipolar I disorder (i.e., bipolar spectrum). Several indices of illness severity differentiate individuals with bipolar disorder from major depressive disorder.