Borderline personality disorder and bipolar II disorder in private practice depressed outpatients.

Bipolar II disorder (BDII) may be confused with borderline personality disorder (BPD) when it is cyclothymic between episodes. The aim of the present study was to determine the prevalence of BPD and to test whether BDII can be distinguished from BPD without difficulty in private practice mood disorder outpatients. Private practice was chosen because it is often the first or second line of treatment of mood disorders in Italy, and many "soft" patients can be found in this setting. Among 63 consecutive unipolar and 50 bipolar II major depressive episode (MDE) outpatients interviewed with the Structured Clinical Interviews for DSM-IV axis I/II disorders (SCIDs), the prevalence of BPD was 6.1% and was significantly higher in BDII patients (12% v. 1.5%). Overall, the rate of BPD diagnosis was very low. BDII was distinguished from BPD without difficulty by DSM-IV criteria. The results suggest that there may be a subgroup of BDII patients with a relatively stable course between episodes (or at least not so unstable as to suggest a BPD diagnosis or comorbidity) and a low comorbidity with BPD, in a setting closer to community patients than university settings. The "usual" BDII patient can be distinguished from the BPD patient.