Problematic boundaries in the diagnosis of bipolar disorder: the interface with borderline personality disorder

It is clinically important to recognize both bipolar disorder and borderline personality disorder (BPD) in patients seeking treatment for depression, and it is important to distinguish between the two. The most studied question on the relationship between BPD and bipolar disorder is their diagnostic concordance. Across studies approximately 10 % of patients with BPD had bipolar I disorder and another 10 % had bipolar II disorder. Likewise, approximately 20 % of bipolar II patients were diagnosed with BPD, though only 10 % of bipolar I patients were diagnosed with BPD. While the comorbidity rates are substantial, each disorder is, nonetheless, diagnosed in the absence of the other in the vast majority of cases (80-90 %). In studies examining personality disorders broadly, other personality disorders were more commonly diagnosed in bipolar patients than was BPD. Likewise, the converse is also true: other axis I disorders such as major depression, substance abuse, and post-traumatic stress disorder are more commonly diagnosed in patients with BPD than is bipolar disorder. Studies comparing patients with BPD and bipolar disorder find significant differences on a range of variables. These findings challenge the notion that BPD is part of the bipolar spectrum. While a substantial literature has documented problems with the under-recognition and under-diagnosis of bipolar disorder, more recent studies have found evidence of bipolar disorder over-diagnosis and that BPD is a significant contributor to over-diagnosis. Re-conceptualizing the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, diagnostic criteria for bipolar disorder as a type of test, rather than the final word on diagnosis, shifts the diagnostician from thinking solely whether a patient does or does not have a disorder to considering the risks of false-positive and false-negative diagnoses, and the ease by which each type of diagnostic error can be corrected by longitudinal observation.