According to this, BPD appears to the most common personality disorder at this particular institution.
(scroll down to see the chart)
http://www.marshall.edu/jrcp/9_1_Adel_Grimm_Mogge.htm
From various other sources, it would appear that BPD is also the hardest disorder to treat.
From this,
http://www.apa.org/monitor/mar04/treatment.aspx
there is a quote:
As a result, people with the disorders often don't seek treatment, and those who do often drop out, he says. For example, people with borderline personality disorder(BPD)--the most commonly treated personality disorder--quit treatment programs about 70 percent of the time.
Another good quote from here:
https://bpdcentral.com/therapists/choose-bpd-therapist/
What all this comes down to is that borderline patients are probably the toughest clients a clinician will ever treat.
I just find it hilarious, and absolutely embarrassing to the profession of therapy, that the most common mood disorder is also the most difficult to treat.
What aggravates me is this notion you hear all the time that mental disorders are "highly treatable" and you just need to "see a professional", when the reality seems to be the exact opposite!