Various forms of depression.

The current subtyping of depression is based on the Diagnostic and Statistical Manual of Mental Disorders, 4th ed, Text Revision (DSM-IV-TR) categorical division of bipolar and depressive disorders. Current evidence, however, supports a dimensional approach to depression, as a continuum/spectrum of overlapping disorders, ranging from bipolar I depression to major depressive disorder. Types of depression which have recently been the focus of most research will be reviewed: bipolar II depression, mixed depression, agitated depression, atypical depression, melancholic depression, recurrent brief depression, minor depressive disorder, seasonal depression, and dysthymic disorder. Most research has focused on bipolar II depression, mixed depression (defined by depression and superimposed manic/hypomanic symptoms), and atypical depression. Mixed depression, by its combination of opposite polarity symptoms, has been found to be common by systematic probing for co-occurring manic/hypomanic symptoms. Mixed depression is a treatment challenge for clinicians, because antidepressants alone (ie, not protected by mood-stabilizing agents) may worsen its manic/hypomanic symptoms, such as irritability and psychomotor agitation, which the Food and Drug Administration (FDA) has listed as possible precursors to suicidality.