Distinguishing between Unipolar Depression and Bipolar Depression: Current and Future Clinical and Neuroimaging Perspectives

Jul 13, 2012Biological psychiatry

Current and future clinical and brain imaging differences between unipolar and bipolar depression

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Abstract

Eight neuroimaging studies have compared individuals with unipolar depression (UD) and bipolar disorder (BD).

Widespread abnormalities in white matter connectivity and hyperintensities are observed more frequently in BD than in UD.
Reductions in habenula volume are noted in BD but not in UD depression.
Distinct patterns of functional abnormalities in brain regions related to emotion regulation and attentional control are identified between the two types of depression.
These findings indicate different underlying processes in emotion regulation, reward, and attentional control associated with BD and UD depression.
There is a need for more neuroimaging studies with larger sample sizes to further differentiate BD from UD.

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Differentiating bipolar disorder (BD) from recurrent unipolar depression (UD) is a major clinical challenge. Main reasons for this include the higher prevalence of depressive relative to hypo/manic symptoms during the course of BD illness and the high prevalence of subthreshold manic symptoms in both BD and UD depression. Identifying objective markers of BD might help improve accuracy in differentiating between BD and UD depression, to ultimately optimize clinical and functional outcome for all depressed individuals. Yet, only eight neuroimaging studies to date have directly compared UD and BD depressed individuals. Findings from these studies suggest more widespread abnormalities in white matter connectivity and white matter hyperintensities in BD than UD depression, habenula volume reductions in BD but not UD depression, and differential patterns of functional abnormalities in emotion regulation and attentional control neural circuitry in the two depression types. These findings suggest different pathophysiologic processes, especially in emotion regulation, reward, and attentional control neural circuitry in BD versus UD depression. This review thereby serves as a call to action to highlight the pressing need for more neuroimaging studies, using larger samples sizes, comparing BD and UD depressed individuals. These future studies should also include dimensional approaches, studies of at-risk individuals, and more novel neuroimaging approaches, such as connectivity analysis and machine learning. Ultimately, these approaches might provide biomarkers to identify individuals at future risk for BD versus UD and biological targets for more personalized treatment and new treatment developments for BD and UD depression.

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Distinguishing between Unipolar Depression and Bipolar Depression: Current and Future Clinical and Neuroimaging Perspectives

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