Depression in bipolar disorder versus major depressive disorder: results from the National Epidemiologic Survey on Alcohol and Related Conditions.

OBJECTIVES: To compare the clinical features and course of major depressive episodes (MDEs) occurring in subjects with bipolar I disorder (BD-I), bipolar II disorder (BD-II), and major depressive disorder (MDD).
METHODS: Data were drawn from the National Epidemiologic Survey on Alcohol and Related Conditions (2001-2002), a nationally representative face-to-face survey of more than 43000 adults in the USA, including 5695 subjects with lifetime MDD, 935 with BD-I and lifetime MDE, and 494 with BD-II and lifetime MDE. Differences on sociodemographic characteristics and clinical features, course, and treatment patterns of MDE were analyzed.
RESULTS: Most depressive symptoms, family psychiatric history, anxiety disorders, alcohol and drug use disorders, and personality disorders were more frequent-and number of depressive symptoms per MDE was higher-among subjects with BD-I, followed by BD-II, and MDD. BD-I individuals experienced a higher number of lifetime MDEs, had a poorer quality of life, and received significantly more treatment for MDE than BD-II and MDD subjects. Individuals with BD-I and BD-II experienced their first mood episode about ten years earlier than those with MDD (21.2, 20.5, and 30.4 years, respectively).
CONCLUSIONS: Our results support the existence of a spectrum of severity of MDE, with highest severity for BD-I, followed by BD-II and MDD, suggesting the utility of dimensional assessments in current categorical classifications.