Unipolar vs bipolar depression: A clinician’s perspective

DSM-5 also requires severity criteria for hypomania that patients with unequivocal hypomanic episodes often do not meet. For example, they may fail to experience flight of ideas or racing thoughts, or engage in activities such as “unrestrained buying sprees, sexual indiscretions, or foolish business investments.” These patients usually describe these mild highs as feeling normal and report a happier mood, more smiles and laughter, increased energy, less sleepiness, increased talkativeness, increased socialization, and improved motivation to complete tasks left undone and projects left unfinished because of the previous depressive episode. These softer (subthreshold) hypomanic episodes are authentic and, if clinicians do not identify them, may lead to misdiagnosis and inappropriate treatment.

Patients who present with depression often fail to report these brief, subthreshold hypomanic episodes or consider them to be irrelevant to their diagnosis and treatment.^12,13 Probing questions can often elicit these unreported highs. For example, a patient with depression should be asked, “Have you had a single good day during the last month?” and “Where were you and what did you do during that day?” Eliciting a history of brief periods of improved mood is the key to differentiating between unipolar and bipolar depression. Screening instruments such as the Mood Disorders Questionnaire¹⁴ and the Bipolar Spectrum Diagnostic Scale¹⁵ may be helpful in distinguishing between unipolar and bipolar depression. However, we offer our thoughts on making that crucial distinction.

Distinguishing between these 2 types of depression

Although it may be difficult to distinguish between unipolar and bipolar depression, especially in the absence of a history of distinct manic or hypomanic episodes, we find the following criteria to be useful in making that determination.

Age of onset. Bipolar spectrum disorders typically begin earlier in life than unipolar depression.^10,16-19 A typical presentation of bipolar disorder in children and adolescents is depression or agitated mixed states with features of both mania and depression, often accompanied by rapid mood cycling.^20,21 Unipolar depression usually begins later in life, and patients do not have a history of significant depressive episodes or mood swings in childhood or adolescence. An important question to ask a patient with a chief complaint of depression is, “How old were you when you first experienced an episode of depression?”

Gender differences. Bipolar spectrum disorders with more subtle (softer) presentations, such as subthreshold highs, occur more often in women than men.²² However, overall rates of bipolar disorder may be slightly higher in men than in women.²³ Unipolar melancholic depression occurs at approximately the same frequency in men and women.²⁴

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