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Is Bipolar Disorder Overdiagnosed? --
on Zimmerman and colleagues' 2008 study 
(written 8/2008) 

Summary:  if you stick to the DSM-IV diagnostic rules, some patients now being considered possibly "bipolar" are indeed "over-diagnosed".  Dr. Zimmerman also found a 30% underdiagnosis rate, and an 86% accuracy rate for bipolar diagnosis overall -- by my calculations below.  Still, we're asking the wrong question, with all this over- versus under-diagnosis talk.  We should be asking "how bipolar are you?" and using a different system to characterize the answer, which includes but goes well beyond the DSM-IV: namely, the Bipolarity Index.  In my opinion....

Page Outline:


Overdiagnosis?

A recent research study found that over half a group of patients who had been told they had bipolar disorder did not meet official standards for that diagnosis. This result was announced widely, including in the Los Angeles Times (May 7, 2008):

Bipolar Disorder Overdiagnosed?
Study Shows Many People Who Are Told They Have the Disorder Don't Meet Standard Criteria

That's odd.  Until recently, most research seemed to show that bipolar disorder was underdiagnosed, not over-diagnosed.

Here's what Zimmerman and colleagues found (and published).  Seven-hundred psychiatric outpatients were asked if they'd ever been told they had bipolar disorder. All 700 also met with a trained interviewer who used a well-respected tool called the Structured Clinical Interview for Diagnosis (SCID), which applies the offical rules for diagnosis in a systematic way. The SCID was used as the standard for determining whether a patient really had bipolar disorder, or not.  The results that got all the press are shown below.

 

SCID Diagnosis
BP DX
BP
Not BP
Total
Yes
63
82
145
No

 

 

 

Total

 

 

 

As you can see, many patients who'd been told they had bipolar disorder did not actually have it, according to the SCID: 82 of them, versus 63 where the SCID diagnosis confirmed what the patient had been told. Over half of the patients had been "overdiagnosed" with bipolar disorder, was the conclusion.

Also found underdiagnosis

Not reported in the press was the next finding, though this was fairly presented in the research team's paper:

 

SCID Diagnosis
BP DX
BP
Not BP
Total
Yes
63
82
145
No
27

 

 

Total
90

 

 

Here we see the percentage of patients who were accurately detected as having bipolar disorder.  Of all those who -- according to the SCID -- did indeed have bipolar disorder, only 70% (63 out of 90) had been told they had that diagnosis. Thirty percent were missed. 

Overall, reasonably accurate?

Finally, one can look at the folks who don't have bipolar disorder as an entire group, to get an idea of what percentage of these folks were incorrectly diagnosed as having bipolar disorder.  For that, look at the numbers in red below:

 

SCID Diagnosis
BP DX
BP
Not BP
Total
Yes
63
82
145
No
27

528

 

Total
90

   610

 

Here we find that the "false positive" rate, of incorrectly calling people "bipolar", was 14% (82 out of 610).  The clinic where these patients are served is correctly recognizing 84% of patients as "not bipolar".  This is far from perfect, but it is in the range of some lab tests used in other areas of medicine.

Over- or under-diagnosis? Wrong question

The real problem is, we're asking the wrong question. The term "overdiagnosis" itself strongly suggests that bipolar disorder is a thing, that you either have or do not have.  Granted, that is how our DSM diagnosis system works, but it was never intended to imply that bipolar disorder is a thing. Evidence increasingly shows that mood problems are caused by many factors (a leading researcher recently stated that there might be as many as 100 risk factors for mood disorders, of which one might need only 5 or so to produce symptoms. In other words, there are many, many different variations possible. No wonder a given treatment can work so well in one person with bipolar disorder, and not at all for someone else).

By contrast, at Harvard's mood clinic, they ask a different question: "how bipolar are you? how much bipolarity do you have?"  I think that's the direction we ought be pursuing. How many bipolar factors do you need to have before antidepressants are so unlikely to work, or so likely to cause significant problems, that you should start with a different treatment instead? Diagnosis should move toward the way they're now doing it at Harvard, using the Bipolarity Index