The mixed state - the name alluding to a mix between depression and mania - has traditionally been viewed (more or less) as combining the dysphoria of depression with the energy of mania. Anger, agitation, restlessness and so forth.
I've been depressed and I know only too well the difference between that "active" depression and the "inactive" kind; if I had to choose, I'd always go for the latter, because at least you're in less danger of doing or saying something you later regret.
However, in the proposals for DSM-5, "mixed" episodes as such will be abolished. Instead, a depressive episode will have "mixed features" if it is associated with at least 3 of 7 symptoms normally seen in (hypo)mania. But - and here's the key novelty - those 7 are only the "good" symptoms of mania. Not things like anger, irritability, insomnia or 'aimless' hyperactivity. (Edit: There are also separate criteria for "mixed" manic and hypomanic episodes).
What will this mean? In a new paper, psychiatrists Perlis, Cusin, and Fava tried to find out. The large STAR*D antidepressant trial recruited people with depression, but it gave everyone the Psychiatric Diagnosis Screening Questionnaire (PDSQ), amongst many other measures. This helpfully included six items on "mania symptoms", which correspond pretty closely to the DSM-V proposed "mixed" features.
Perlis et al found that depressed patients who reported experiencing these "mixed" items had a better response to antidepressant treatment. The more mixed symptoms, the more likely they were to get better on the common SSRI citalopram, even adjusting for other variables.
That's the exact opposite of what you'd expect from a measure of "mixed states", as these are thought to be less responsive to antidepressants - maybe even caused by them. There was no placebo group, so it's unclear why they got better, but either way, it's unexpected; the authors declare themselves "surprised". Hmm. What a mystery...
Or maybe not. These manic symptoms are all things that you're not when you're depressed. The 6 items actually make a good summary of what depression, even agitated depression (except maybe #6) isn't.
So, one interpretation of these results is that people who endorsed these items just weren't depressed, at some point in the 6 months prior to doing the PDSQ. Assuming they were depressed at other points that means their mood was variable over time.
People whose depression is variable might well be more likely to recover than the ones whose depression was unrelenting.
Now Perlis et al do consider this -
further models were fit incorporating the IDS-C30 pleasure and reactivity items; results were essentially unchanged indicating that they are unlikely to be confounded by mood variability per se...But this assumes that the IDS-C30 questionnaire is a good measure of mood variability in this sample. Maybe it's not, and these data are telling us so. I'd have said that's more likely than the idea that these people were actually both cheerful and depressed at the same time, which seems like a contradiction in terms.
Maybe I'm wrong, and these people did feel that, but the problem is, we can't tell, because no-one actually sat down and asked these people what was going on, or heard their account of what they meant by ticking both the "depressed" and "manic" boxes.
Did they experience a strange mixed emotional state in which they simultaneously depressed and happy? Did their mood see-saw from one day to the next? Or weekly, monthly? Were they depressed in the day and happier in the evening? Were they depressed, then back to normal, leading them to see the normal as a 'high', by comparison with the lows? Were they depressed when sober and happy when drunk? Vice versa? Are they experiencing normal ups and downs and interpreting them as 'mood swings' because they've become convinced, for whatever reason, that they have a mood disorder? Did they just have a poor command of English and weren't really trying to say what the highly-educated investigators assume they were?
Don't seek, and ye shan't find.
It's not great news for the DSM-5 proposals, either way, although defenders could hold out hope that the differences between those criteria and the PDSQ measure might mean the DSM-5 will perform better...
Perlis, R., Cusin, C., and Fava, M. (2012). Proposed DSM-5 mixed features are associated with greater likelihood of remission in out-patients with major depressive disorder Psychological Medicine, 1-7 DOI: 10.1017/S0033291712000281