Objective: There is growing clinical and epidemiological evidence that undiagnosed bipolar features are source of clinical heterogeneity in major depressive disorder (MDD). This study examined and compared the prevalence and correlates of lifetime major depressive episode plus subthreshold hypomania D(m) with pure MDD, bipolar II disorder, and bipolar I disorder.
Method: Data were drawn from the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), a large cross-sectional survey (n=43,093) representative of the U.S. population.
Results: The lifetime prevalences were 2.53% for D(m), 1.12% for bipolar II disorder, 2.19% for bipolar I disorder and 10.70% for pure MDD. All bipolar disorders (i.e., D(m), BP-II, and BP-I) were half as frequent as MDD. Lifetime and 12-month psychiatric comorbidity, course and clinical characteristics, symptoms, health status and treatment-seeking rates were significantly different in participants with lifetime D(m) when compared to participants with pure MDD, but not when compared to participants with bipolar II disorder.
Limitations: Subthreshold hypomania diagnostic was based on the lifetime presence of at least one of the three screening questions for criterion A for hypomania, without a lifetime history of manic or hypomanic episode. This narrow definition, both in terms of the choice of hypomanic symptoms and their duration, could have led to an underestimation of the proportion of participants with a lifetime history of D(m). In addition, the cross-sectional nature of this study does not allow causal associations to be drawn.
Conclusions: Our data confirm and extend evidence of the clinical significance and validity of a subthreshold bipolarity-specifier applied to individuals with DSM-IV MDD. Major depression with subthreshold hypomania could be more accurately incorporated into the bipolar II disorder diagnosis.
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