Borderline personality disorder and bipolar are two separate diagnoses that in some cases appear very similar, and which can in some cases go together. Both involve patients cycling from manic moods, characterized by high energy, positive emotions, and impulsive behavior, to depressive moods where the person feels sad, irritable, and lethargic. Patients with borderline personality disorder tend to be diagnosed with bipolar somewhat more frequently than patients with other personality disorders, indicating a possible link between the two. The underlying causes of the two disorders do appear to be different, however; bipolar appears to be tied to chemical imbalances in the brain, while borderline personality disorder seems to be tied closely to delayed personal and emotional development.
The symptoms of borderline personality disorder and bipolar can often be the same, though there are factors that differentiate them. The primary feature of both disorders is a shift from manic to depressive moods; patients can go from feeling happy, elated, and energetic to having low energy and feeling negative. The presentation of these symptoms differs, however, in how frequently patients shift moods; those with bipolar will typically maintain the same mood for weeks or months before having a shift, while people with borderline personality disorder can transition between moods very rapidly, daily or even hourly.
There appears to be some possible connection in the likelihood of being diagnosed with both borderline personality disorder and bipolar. Studies have found that there is a higher chance that one will be found to have bipolar in conjunction with borderline personality than with other types of personality disorders. The connection is not considered strong, however, and may also be the result of incorrect diagnosis due to the similar symptoms of the two.
Though borderline personality disorder and bipolar disorder can often present in similar ways, it is generally agreed upon that the root causes of each are very different. Episodes of mood swings in bipolar patients, for example, often seem to occur for no apparent reason; this is indicative of the issues with brain chemistry thought to trigger them. Those with borderline personality disorder, on the other hand, often experience changes in mood in response to environmental or situational stressors. This is typically attributed to the fact that these patients are considered to suffer from a lack of emotional maturity which causes them to view situations in black and white, making them very sensitive and temperamental.