Nosologic confusion?
Exactly.
The comorbidity I'm sure to some degree has to do with the fact that both look similar. I best some of the people in the comorbidity studies were misdiagnosed.
Add to the confusion Cyclothymia, where one has symptoms of bipolar but not enough to meet enough criteria of bipolar mania or a major depressive episode.
Several similar symptoms: The age where the person does behavior that could be considered dangerous start around the same time where it is reasonable for a diagnosis of either bipolar disorder or borderline PD. Both are characterized by impulsivity, emotional dysregulation in borderline can look like irritability in bipolar disordorder, grandiosity could look like black and white thinking seen with borderline.
How do I try to differentiate the two?
Look at both disorders and try to parse out the differences.
1) Bipolar disorder is episodic where the manic/hypomanic episodes will last at least days. Compared to borderline where it's pretty much there all the time.
2) Lack of sleep. Yes it can happen in both, but if the person sleeps soundly even during periods where they show irritability, impulsivity etc., that leans towards borderline PD. (And yes, one can still be manic or hypomanic and still sleep fine though it's rare)
3) Self-mutilation especially in order to decrease the degree of emotional pain strongly pulls this to borderline PD.
4) Increased goal directed activity pushes this more so on the order of bipolar disorder.
5) A strong history of invalidation, abuse, lack of a supportife environment as a child, and good parenting moderately leans on borderline PD.
6) Impulsivity on the order of extreme grandiosity (e.g. I had a patient that opened up a gym all on credit card payments, invited all his friends and family and had them brought there in stretch limos, and had spotlights and a paid a tv celebirty to host the opening of the gym...and no the gym was not expected to rake in that much money) strongly hints of bipolar DO.
7) Psychological testing could help. An MMPI, YMRS, etc.
8) Get as much history as you can. Hospitalizations would be very important because the person may have been full-blown manic during the hospitalization and if records support this, that would strongly support bipolar disorder.
There is a spectrum where several disorders can look like each other.
A person with poor sleep, easy distractibility, faltering relationsihps, "racing thoughts" can be bipolar disorder, generalized anxiety disorder, borderline PD, and/or ADHD. Heck it could be ALL OF THEM (though that would be rare). What psychiatrists call racing thoughts is not what patients know to call racing thoughts. Someone with excessive anxiety could call it "racing thoughts." Remember, they don't have the training you and I have. Someone who diagnoses a patient as bipolar disorder simply on the mention of "racing thoughts" is in my opinion not too bright and is trying to cut corners. (That and the classic "Do you hear voices?" "Yeah I hear your voice." "Oh then you have schizophrenia." I kid you not a resident in my program did that all the time and no attending was willing to correct him. He ended up diagnosing everyone with psychosis.)
If someone says they have racing thoughts, try to further parse what they really mean. Ask open-endedly what they mean by racing thoughts. If they can't give you the information you need from that question, ask them the following: "When you say you have racing thoughts, do you mean you feel anxiety, like as if you're scared?" (suggests anxiety not bipolar disorder) "When you say you racing thoughts, do you mean you feel as if your thoughts are going so fast to the point where it seems uncomfortable?" (suggests bipolar disorder) "By racing thoughts, do you mean you have problems sitting still and if you don't move around you might feel like you're trapped?" (suggests ADHD).
Borderline PD may also describe their problems as racing thoughts but from experience it seems to be more so from a frantic fear of abandonment, problems controlling anger, and intrapsychich splitting.
Cases:A 30 year old Caucasian male with marriage problems including accusing his wife of cheating on him. He never experienced a manic episode but frequently feels that she is cheating on him, poor sleep, and irritability. He meets the chronicity pattern of cyclothymia.
There is no history of abuse, he came from a stable family (parents did not divorce, they are well educated, he is close with his parents).
Turned out that Lamictal 50 mg Q daily stabilized all his symptoms within 3 weeks of treatment (takes 2 weeks to get to 50 mg Qdaily!). Dx: Cyclothymia.
Problems: because he never met the criteria for bipolar disorder, for years psychiatrists and psychologists all told him this was not an Axis I disorder and he went through over 2 years of psychotherapy with little to no benefit.
Remember: cyclothymia exists!
Case: 32 year old Caucasian female with a history of self mutilation (but she no longer does this thanks to DBT), has 5 children, gets no child support, excessive irritability, poor sleep, poor anger management, impulsivity (would stand on cars while they were in motion because it was fun), and complains of racing thoughts.
I parsed out the chronicity pattern of her behaviors. IMHO she had both. She always had emotional dysregulation, the self-mutilation strongly suggests she had borderline PD, but she also had patterns where poor sleep, increased energy, impulsivity, and goal directed activity got worse and lasted weeks.
DX: Bipolar I disorder, most recent episode manic without psychotic features and borderline PD.
Tx: Lamcital 200 mg Q daily. Now there are only symptoms of borderline PD. No episodes of poor sleep, increased energy, and increased goal directed activity. She occasionally does impulsive behavior but not on the extreme it used to occur. She is getting DBT.
I mentioned before that trying to figure out what disorders someone has can be like trying to figure out what's in a dish of food.
Some cases are easy. A bowl of oatmeal with cinnamon. Easy. Pizza with mushrooms on it. Easy
What about a dish where there's meat that could pass for veal or marinated pork? What about the sauce? Figuring out what's in a sauce or gravy can be tough. What kind of cheese is sprinkled on it that's already drown in the sauce?
Diagnosing someone with multiple disorders can become like the latter example. With time, experience, and a true desire to diagnose for real and not cut corners, you can get there.
Start the video at 4 minutes.
http://www.youtube.com/watch?v=y--WVBbElPM&feature=fvw