Background: Recently, there has been a rebirth of studies on depressive mixed state (DMX), defined as a major depressive episode (MDE) plus few concurrent hypomanic symptoms. It is still unclear how to best define DMX. The study's aim was to test a categorical versus a dimensional definition of DMX.
Methods: Consecutive 260 bipolar II disorder and 173 unipolar MDE outpatients were interviewed with the Structured Clinical Interview for DSM-IV, when presenting for MDE treatment (drug-free). Hypomanic symptoms during index MDE were systematically assessed and graded by a hypomania rating scale (Hypomania Interview Guide, HIG). Different cutoffs of the HIG to define DMX were tested versus a categorical definition of DMX (requiring more than two concurrent hypomanic symptoms, DMX3). Sensitivity and specificity for predicting bipolar II diagnosis were compared. The best definition of DMX based on the HIG was also compared to DMX3 versus typical bipolar variables (early onset, many recurrences, atypical features, bipolar family history).
Results: An HIG cutoff of 8 had a specificity for predicting bipolar II diagnosis similar to that of DMX3. HIG>8 was strongly associated with bipolar family history (an important external diagnostic validator), and DMX3 was significantly associated with more bipolar variables (including bipolar family history).
Limitation: The interview was done by a single interviewer.
Conclusions: Similar specificity for predicting bipolar II disorder diagnosis and a similar strong association with bipolar family history suggest that a categorical and a dimensional definition of DMX could have similar validity. However, the dimensional definition (based on the scoring of a hypomania rating scale) could lead to a better assessment of hypomanic symptoms, resulting in more correct diagnoses of DMX.