Borderline personality-bipolar spectrum relationship.

BACKGROUND: The relationship between borderline personality disorder (BPD) and bipolar disorders, especially bipolar-II disorder (BP-II), is unclear. Several reviews on the topic have come to opposite conclusions, i.e., that BPD is a bipolar spectrum disorder or instead that it is unrelated to bipolar disorders. Study aim was to find which items of BPD were related to BP-II, and which instead had no relationship with BP-II.

STUDY SETTING: An outpatient psychiatry private practice, more representative of mood disorders usually seen in clinical practice in Italy. INTERVIEWER: A senior clinical and mood disorder research psychiatrist.

PATIENT POPULATION: A consecutive sample of 138 BP-II and 71 major depressive disorder (MDD) remitted outpatients. ASSESSMENT INSTRUMENTS: The Structured Clinical Interview for DSM-IV Axis I Disorders-Clinician Version (SCID-CV) was used for diagnosing, the SCID-II Personality Questionnaire was used by patients to self-assess borderline personality traits. Interview methods: Patients were interviewed with the SCID-CV to diagnose BP-II and MDD. The questions of the Personality Questionnaire relative to borderline personality were self-assessed by patients. As clinically significant distress or impairment of functioning was not assessed by the questionnaire, a diagnosis of borderline personality disorder could not be made, but borderline personality traits (BPT) could be assessed (i.e., all DSM-IV BPD items but not the impairment criterion).

RESULTS: BPT items were significantly more common in BP-II versus MDD. The best combination of sensitivity and specificity for predicting BP-II was found by using a cutoff number of BPT items > or =5: specificity was 71.4%, sensitivity was 45.9%. BPT (defined by > or =5 items) was present in 29.5% of MDD and in 46.3% of BP-II (p=0.019). Logistic regression of BP-II versus BPT items number found a significant association. Principal component factor analysis of BPT items found two orthogonal factors: "affective instability" including unstable mood, unstable interpersonal relationships, unstable self-image, chronic emptiness, and anger, and "impulsivity" including impulsivity, suicidal behavior, avoidance of abandonment, and paranoid ideation. "Affective instability" was associated with BP-II (p=0.010), but "impulsivity" was not associated with BP-II (p=0.193). Interitem correlation was low. There was no significant correlation between the two factors.

DISCUSSION: Study findings suggest that DSM-IV BPD may mix two sets of unrelated items: an affective instability dimension related to BP-II, and an impulsivity dimension not related to BP-II, which may explain the opposite conclusions of several reviews. A subtyping of BPD according to these dimensions is supported by the study findings.