Data from a long-term study indicate that borderline personality disorder and bipolar disorder do not commonly coexist, a finding with important implications for treatment, according to an article in the July issue of The American Journal of Psychiatry.

The personality disorder is a long-term, pervasive pattern of impulsive behavior, instability and changeable mood. Whether it is a variant of bipolar disorder is the focus of the article, whose lead author, John G. Gunderson, M.D., is medical director for the Borderline Personality Disorder Treatment Center at McLean Hospital, Belmont, Massachusetts.

The study found only modest connections to bipolar disorder among 196 patients with confirmed diagnosis of borderline personality disorder. The rate of co-occurring bipolar disorder in these patients was 19 percent. In contrast, the rate for co-occurring bipolar disorder in patients with other personality disorders was 8 percent.

Among patients with a personality disorder who did not have bipolar disorder at the beginning of the study, 8 percent of the borderline personality patients developed bipolar disorder over the next 4 years compared with 3 percent of patients with other personality disorders.

Despite these differences, the rates of co-occurring bipolar disorder in borderline personality patients remained under 20 percent. This low frequency has important implications for treatment because many patients with borderline personality treatment receive only a diagnosis of bipolar disorder and the two diagnoses generally are treated with different approaches. Psychosocial interventions are important in the treatment of the personality disorder, whereas medication is generally the first choice for bipolar disorder.

“The diagnosis of borderline personality disorder arose from psychoanalytic psychotherapy practice, whereas bipolar disorder is the subject of intensive neurobiological research and psychopharmacological treatment,” stated Robert Freedman, MD, journal editor-in-chief. “This study is an important step in examining the extent of overlap between the two disorders.”

The co-occurrence of bipolar disorder did not worsen the course of borderline personality disorder over 4 years. Remission occurred in roughly two thirds of both borderline personality disorder patients with and without bipolar disorder.

In an accompanying editorial, Michael H. Stone, MD, of Columbia University noted the article’s “more balanced position on the controversy” about the relationship of borderline personality to bipolar disorder. He suggested that the moderately higher rates of bipolar disorder in patients with borderline personality disorder may indicate a subgroup of borderline personality patients with higher genetic risk for bipolar disorder.