Mixed state discrimination: a DSM problem that won׳t go away?

Background: DSM׳s replacement of 'mixed episodes' with 'mixed features' has ironically created a specifier, which potentially lacks specificity because it overlooks two key symptoms: psychomotor agitation and distractibility. Therefore, the present study examined the presence of psychomotor agitation and distractibility across the mood disorder spectrum.

Methods: Two hundred patients were diagnosed and assigned to one of three groups (depression, bipolar spectrum disorder (BDspectrum) and bipolar disorder) based on clinical evaluation by a psychiatrist. On the basis of MDQ scores, the depression group was then further subdivided into two groups: unipolar depression (UP) and mixed depression (UPmix). These four groups were then compared to examine the relative distribution of psychomotor agitation and distractibility. Participants underwent a clinical evaluation by a psychiatrist and completed a series of questionnaires.

Results: Increased distraction, racing thoughts, and increased irritability were the most commonly reported manic symptoms amongst the unipolar depression group. Further, UPmix and BDspectrum had significantly higher psychomotor agitation and distractibility than the other two groups.

Limitations: The present study depended on self-report measures and did not include standardised measures of distractibility and psychomotor agitation. Future research needs to examine pure unipolar patients without any manic symptoms to clarify further how different this group would be from those with mixed features.

Conclusions: The present findings suggest that distractibility and psychomotor agitation may represent the core of mixed states, as they are more common in patients with mixed depression and bipolar spectrum disorder than patients diagnosed with unipolar depression and bipolar I disorder. Future research and clinical implications are discussed.