As psychotic agitated depression is now a well-described form of mixed state during the course of bipolar I disorder, we sought to investigate the diagnostic validity of a new definition for agitated (mixed) depression in bipolar II (BP-II) and major depressive disorder (MDD).

Three hundred and thirty six consecutive outpatients presenting with major depressive episodes (MDE) but without history of mania were evaluated with the Structured Clinical Interview for DSM-IV when presenting for the treatment of MDE. On the basis of history of hypomania they were assigned to BP-II (n = 206) vs. MDD (n = 130). All patients were also examined for hypomania during the current MDE. Mixed depression was operationally defined by the coexistence of a MDE and at least two of the following excitatory signs and symptoms as described by Koukopoulos and Koukopoulos (Koukopoulos A, Koukopoulos A. Agitated depression as a mixed state and the problem of melancholia. In: Akiskal HS, editor. Bipolarity: beyond classic mania. Psychiatr Clin North Am 1999;22:547–64): inner psychic tension (irritability), psychomotor agitation, and racing/crowded thoughts. The validity of mixed depression was investigated by documenting its association with BP-II disorder and with external variables distinguishing it from unipolar MDD (i.e., younger age at onset, greater recurrence, and family history of bipolar disorders). We analyzed the data with multivariate regression (STATA 7).

MDE plus psychic tension (irritability) and agitation accounted for 15.4%, and MDE plus agitation and crowded thoughts for 15.1%. The highest rate of mixed depression (38.6%) was achieved with a definition combining MDE with psychic tension (irritability) and crowded thoughts: 23.0% of these belonged to MDD and 76.9% to BP-II. Moreover, any of these permutations of signs and symptoms defining mixed depression was significantly and strongly associated with external validators for bipolarity. The mixed irritable-agitated syndrome depression with racing-crowded thoughts was further characterized by distractibility (74–82%) and increased talkativeness (25–42%); of expansive behaviors from the criteria B list for hypomania, only risk taking occurred with some frequency (15–17%).

These findings support the inclusion of outpatient-agitated depressions within the bipolar spectrum. Agitated depression is validated herein as a dysphorically excited form of melancholia, which should tip clinicians to think of such a patient belonging to or arising from a bipolar substrate. Our data support the Kraepelinian position on this matter, but regrettably this is contrary to current ICD-10 and DSM-IV conventions. Cross-sectional symptomatologic hints to bipolarity in this mixed/agitated depressive syndrome are virtually absent in that such patients do not appear to display the typical euphoric/expansive characteristics of hypomania—even though history of such behavior may be elicited by skillful interviewing for BP-II. We submit that the application of this diagnostic entity in outpatient practice would be of considerable clinical value, given the frequency with which these patients are encountered in such practice and the extent to which their misdiagnosis as unipolar MDD could lead to antidepressant monotherapy, thereby aggravating it in the absence of more appropriate treatment with mood stabilizers and/or atypical antipsychotics.