The prevalence of cyclothymia in borderline personality disorder.

Sixty patients with personality disorders were evaluated by several different diagnostic instruments to determine the prevalence of cyclothymia in borderline personality disorder (BPD) and in other personality disorders (OPD). Cyclothymia occurred more frequently in BPD than in OPD, regardless of which diagnostic system was used. In contrast, the prevalence of major, minor, and intermittent depression, hypomania, and bipolar disorder was not significantly different in BPD as compared with OPD. Cyclothymic borderlines and noncyclothymic borderlines could not be distinguished on behavioral or functional measures. These results have implications for the diagnostic validity of both BPD and cyclothymia.