Depressive mixed state: a feature of the natural course of bipolar II (and major depressive) disorder?

BACKGROUND: Depressive mixed state (DMX), i.e., a combination of hypomanic and depressive symptoms during the same episode, has recently seen a rebirth of studies after Kraepelin's description. Kraepelin observed, in an inpatient sample, that DMX was related to the number of episodes and to duration of manic-depressive insanity (illness). STUDY AIM: The aim was to test Kraepelin's observations in a very different sample.
METHODS: 563 consecutive outpatients with major depressive episode (MDE)--320 with bipolar II disorder and 243 with major depressive disorder--were interviewed, in a private practice, by the Structured Clinical Interview for DSM-IV as modified by Benazzi and Akiskal (2003). Hypomanic symptoms during MDE were systematically assessed in patients while off psychoactive drugs. DMX was dimensionally defined, following Akiskal and Benazzi (2003), as an MDE plus 3 or more combined hypomanic symptoms. Kraepelin's examples of DMX, i.e., agitated depression (MDE plus psychomotor agitation) and depression with flight of ideas (MDE plus racing thoughts) were also tested. Univariate and multivariate logistic regression was used to study associations.
RESULTS: DMX was present in 49.5% of the patients. Multiple logistic regression of DMX versus MDE recurrences and duration of illness, controlled for age, found a strong and significant association only between DMX and duration of illness. The same association was found between agitated depression and duration of illness (but not in depression with racing thoughts). LIMITATION: There was only a single interviewer. DISCUSSION: The findings support Kraepelin's observation of a link between DMX and durations of illness, but not that between DMX and recurrences. Onset of DMX could be more related to the natural course of manic-depressive illness than to a kindling process.