Subthreshold bipolar disorder is a set of bipolar symptoms that don’t quite meet the definition of bipolar disorder. Think of it as “bipolar lite.” There is no single, agreed-upon definition for this disorder. For instance, if you need 3 symptoms to meet the criteria for a manic episode, sub-threshold bipolar disorder might be met with fewer symptoms, or require that the symptoms be met for a lesser period of time.

In other words, it’s a way of characterizing people as having a potential mental illness — but who do not yet have one.

The DSM — the reference book that defines mental disorders — is under revision for a new edition to be published next year. One of the considerations is subthreshold bipolar disorder.

Yet Mark Zimmerman, MD points out that this is probably a bad idea. And I’d have to agree.

He notes that, “The DSM-5 Mood Disorders Work Group is considering expanding the boundary of bipolar disorder by reducing the duration required to define a hypomanic episode.”

The problem with lowering the threshold for any disorder is that you will inevitably be saying more people have this problem — or potential problem — than actually do. The number of false positives will skyrocket, as Dr. Zimmerman notes:

As described in my recent Commentary, however, the results of 4 prospective 3- to 17-year follow-up studies indicated that, while subthreshold bipolarity was a risk factor for the future emergence of bipolar disorder, the vast majority of individuals did not develop bipolar disorder.

That means while it may help identify a few people who do go on to develop bipolar disorder, most people don’t.

Worse yet is that most mental health professionals wouldn’t dream of medicating a person with just the potential of a future disorder. So the end result for these people should be the same — watchful waiting.

But since most healthcare professionals who treat bipolar disorder are physicians and family doctors — not mental health professionals — do you think they’d understand and appreciate this subtle difference? Or would they just see, “Hey, I can now bill for subthreshold bipolar disorder, let’s put this person on some medication just to be certain.” Never mind the evidence to the contrary:

Yet, the literature reviews advocating the expansion of the diagnostic boundary have not identified a single controlled study of the efficacy of mood stabilizers in the treatment of subthreshold bipolar disorder. The risk of medically significant side effects, on the other hand, is well established.

I firmly stand against any wholesale expansion of mental disorders’ definitions to include the mere potential of that disorder. Lots of everyday, normal behaviors or symptoms can look like mental disorders for short periods of time.

Such a slippery slope would be rife for abuse by well-meaning and well-intended healthcare professionals, leading to even more people being placed on psychiatric medications that will probably not help much — and could potentially hurt — people who have no mental illness in the first place.

Subthreshold Bipolar Disorder