Recent findings from an American research team indicate that doctors may underdiagnose cases of borderline personality disorder (BPD) and overdiagnose cases of bipolar disorder, a second severe mental health condition that has certain features in common with BPD. Doctors and researchers are well aware that borderline personality disorder and bipolar disorder share an overlapping set of symptoms. In fact, the two conditions sometimes appear together in the same individual. In a study review published in January 2015 in the journal Borderline Personality and Mood Disorders, researchers from two U.S. institutions sought to determine if cases of BPD are underdiagnosed by American doctors. They also sought to determine if doctors overdiagnose the presence of bipolar disorder. BPD and Bipolar Disorder People with borderline personality disorder have long-term personality traits that seriously impede their ability to do such things as maintain control over changes in emotion or mood, maintain healthy relationships with friends or loved ones, and\/or avoid frequent involvement in reckless or impulsive behavior. The condition is well-known for its diverse presentation of possible symptoms, and affected individuals can have a range of problems that include highly volatile changes in mood, an inability to develop a firm sense of self, recurring participation in specific reckless (and possibly harmful) activities, frequent thoughts of suicide or actual suicidal behavior, frequent self-injury not intended to result in loss of life, prominent fears of being abandoned by others and bouts of anger that don\u2019t make sense for a given social context. People with bipolar disorder have any one of several conditions that produce episodes of mild to severe depression and moderate to extreme mania. Specific conditions in this category of illness include bipolar I disorder (classic \u201cmanic depression\u201d), bipolar II disorder (which features less extreme episodes of mania) and cyclothymic disorder (which features less extreme episodes of depression and mania). Some affected individuals experience overlapping bouts of mania and depression; in addition, some individuals cycle from depression to mania (and back again) with unusual frequency. Overlap of Symptoms Two general types of symptoms commonly appear in people affected by borderline personality disorder and people affected by bipolar disorder: increased involvement in impulsive behavior and unusually extreme changes in mood. In addition, substantial numbers of individuals with BPD may actually qualify for a secondary diagnosis of bipolar disorder. In a study published in December 2014 in the Journal of Affective Disorders, a team of Swiss researchers assessed the rate of bipolar disorder in individuals diagnosed with borderline personality disorder. These researchers provisionally concluded that slightly more than half of all BPD-affected people may have a diagnosable case of some form of bipolar disorder. (Similar numbers of people with BPD may have diagnosable symptoms of ADHD, a condition also noted for the presence of unusually impulsive behavior.) Do Doctors Underdiagnose BPD? In the study published in Borderline Personality and Mood Disorders, researchers from Harvard-affiliated McLean Hospital and Brown University\u2019s Alpert School of Medicine used an analysis of the findings of a range of previous studies to gauge whether doctors in the U.S. underdiagnose cases of borderline personality disorder and overdiagnose cases of bipolar disorder. The researchers pursued this line of inquiry, in part, out of concern that at least some people diagnosed with bipolar disorder might better fit the criteria used to diagnose BPD. The researchers preliminarily concluded that it\u2019s relatively difficult for doctors to diagnose all forms of personality disorder. (There are nine such conditions in addition to BPD.) Factors that contribute to this difficulty include the length of time over which the symptoms of a personality disorder can appear and the diversity of symptoms present in any affected individual. For these and other reasons, doctors under common time constraints may fail to recognize the presence of borderline personality disorder or any other personality disorder. With respect to BPD in particular, the researchers also concluded that detailed interviews with patients typically lead to a substantially higher rate of diagnosis than the less structured approaches used by most physicians. (One study reported a rate of diagnosis from detailed interviews more than 30 times higher than the rate associated with the briefer clinical interviews conducted by the average doctor.) Overall, the study\u2019s authors concluded that borderline personality disorder is widely underdiagnosed in the U.S. and other countries. In addition to basic diagnostic difficulties, contributing factors to this situation include a relative lack of experience dealing with patients possibly affected by BPD, the relative lack of medication-based treatments for BPD (compared to bipolar disorder) and a conscious or unconscious desire to avoid giving a potentially stigmatizing BPD diagnosis.