In reference to gmayno's comment and in agreeing with verso's comment - if anything, BPD is rarely "misdiagnosed," but more often than none, is "mistaken" for another disorder, most often bipolar or aspbergers or something of the like. Another interesting snippet I found:
"How Often is BPD Misdiagnosed?
Many people with BPD have stories of misdiagnosis, but how often does it really happen? Unfortunately, there is very little research to draw from, but at least one study suggests that BPD does get misdiagnosed at fairly high rates. A study by researchers at the University of North Texas and Brown University found that nearly 40% of people with BPD in the study sample had previously received a misdiagnosis of bipolar disorder.
There have also been reports of people with BPD being misdiagnosed with psychotic disorders and Asperger's disorder (a type of developmental disorder on the autism spectrum), although there is no research exploring cases of this nature. But, more often, people with BPD report that they received a diagnosis of a mood or anxiety disorder long before their borderline symptoms were recognized. This is not really misdiagnosis so much as "missed diagnosis." Clinicians tend to miss the BPD symptoms at the outset of treatment, so they correctly diagnose other psychiatric problems but fail to catch the BPD diagnosis.
Why is BPD so Difficult to Diagnose?
Why might a BPD diagnosis be missed? There are likely a few different factors at play. First, BPD symptoms are often not evident at the outset of a therapeutic relationship. Many people with BPD do not really "show" their symptoms in more superficial relationships (such as with acquaintances), or in the early stages of relationships.
As a result, a clinician may miss the diagnosis because in the context of therapy the symptoms do not appear. To be clear, it is not that the person with BPD is intentionally hiding their symptoms, but rather that the interpersonal symptoms of BPD really only become evident in the context of close relationships (i.e., the relationships that the person with BPD has more investment in and is more afraid of losing).
To compound this problem, people with BPD may drop out of treatment at relatively high rates. So, if the person with BPD is not showing symptoms early in the therapy, and is also not staying in therapy for long, they may see a string of providers who never get a glimpse of the symptoms.
Another problem may be in the diagnostic criteria for BPD. Many experts believe that the criteria we use to diagnose BPD are too vague and overlapping with other disorders. They argue that BPD has a very high rate of comorbidity (i.e., co-occurrence with other disorders) because our current way to diagnose BPD is not precise enough. Problems with the precision and clarity of the criteria could also lead to misdiagnosis."
HTTP://bdd.about.com
Super good read. I love reading and learning about this stuff. So fascinating.