For years, a consensus had emerged that bipolar disorder was being under-diagnosed (e.g., Akiskal et al., 2000, Bowden, 2001, Ghaemi et al., 1999, Ghaemi et al., 2000, Hirschfeld, 2001, Lish et al., 1994, Manning et al., 1997 and Perugi et al., 1998). A recent report, however, showed a dramatic shift in this trend, with the rate of bipolar diagnosis among outpatient office-based visits doubling in the last decade among adults and rising nearly 40-fold among children and adolescents (Moreno et al., 2007). A subsequent study from our group provided evidence of potential misdiagnosis of bipolar disorder (Zimmerman et al., 2008).
Little work has considered factors associated with the possible overdiagnosis of bipolar disorder. One source of error may involve confusing symptoms of borderline personality disorder with bipolar disorder. Although the disorders are clearly distinct as defined by the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 2000), a number of shared phenomenological features make the latter hypothesis plausible. Affective instability is a core feature of both disorders, albeit the nature and course of this instability may differ ( Henry et al., 2001 and Koenigsberg et al., 2002). The difficulty controlling anger often seen in patients with borderline personality disorder might be confused with the irritability of a manic episode ( American Psychiatric Association, 2000). Impulsivity is a hallmark of borderline personality disorder, but is also common in patients with bipolar disorder even outside of episodes ( Links et al., 1999, Swann et al., 2003 and Zanarini, 1993). Both disorders are also often characterized by recurrent suicide attempts ( Fyer et al., 1988, Ruggero et al., 2007 and Zanarini et al., 2008) and problematic social functioning ( American Psychiatric Association, 2000, Bauwens et al., 1991, Dion et al., 1988, Fagiolini et al., 2005 and Weinstock and Miller, 2008). Similarities between the two disorders have even prompted some to question whether they belong to the same spectrum, although evidence for this hypothesis remains mixed ( Akiskal et al., 1985, Akiskal, 2002, Benazzi, 2008, Deltito et al., 2001, Gunderson et al., 2006, Koenigsberg et al., 2002, Mackinnon and Pies, 2006, Magill, 2004, Paris et al., 2007, Smith et al., 2004 and Wilson et al., 2007).
In this report from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project (Zimmerman, 2003) we assess the extent to which specific features of borderline personality disorder may put a patient at risk of being misdiagnosed with bipolar disorder. Based on the similar phenomenological features discussed above, we hypothesized that the borderline criteria reflecting affective instability, anger, impulsivity, recurrent suicidal behavior, and interpersonal instability would be most associated with bipolar misdiagnosis.
