The purpose of this study was to test whether borderline personality disorder is a variant of bipolar disorder by examining the rates of co-occurrence in both disorders, the effects of co-occurrence on a longitudinal course, and whether the presence of either disorder confers the risk for new onsets of the other.
A prospective repeated-measures design with reliable independent diagnostic measures and 4 years of follow-up was used to assess 196 patients with borderline personality disorder and 433 patients with other personality disorders.
Patients with borderline personality disorder had a significantly higher co-occurrence of bipolar disorder (19.4%) than did patients with other personality disorders. However, this co-occurrence did not appear to affect the subsequent course of borderline personality disorder. Although only 8.2% of the borderline personality disorder patients developed new onsets of bipolar disorder, this rate was higher than in patients with other personality disorders. Patients with other personality disorders with co-occurring bipolar disorder generally had more new onsets of borderline personality disorder (25%) than did patients with other personality disorders without co-occurring bipolar disorder (10%).
A modest association between borderline personality disorder and bipolar disorder is reported.