A colleague approached me and said that she was referring a patient to the partial hospital program who had borderpolar. Having not previously heard this term, clarification was sought, and it was explained that the patient had both borderline personality disorder and bipolar disorder. My colleague further explained that this term is frequently used in the psychiatrist chat room she visits as a shorthand for patients with both disorders who are severely ill and have high levels of psychosocial morbidity. A Pubmed search on the term borderpolar did not turn up any citations.
Both bipolar disorder and borderline personality disorder (BPD) are significant public health problems. Both disorders are associated with impaired functioning, high utilization of psychiatric services, high rates of substance use disorders, and suicidality. Despite the psychosocial morbidity and risk for premature mortality, both disorders are frequently underdiagnosed. As a result, calls for improved recognition have been voiced for both disorders.1,2
For years there has been debate as to how to conceptualize the relationship between BPD and bipolar disorder. Some experts have suggested that BPD is part of the bipolar spectrum. Review articles have summarized the evidence supporting and opposing the bipolar spectrum hypothesis, with most of the recent reviews concluding that BPD and bipolar disorder are valid and distinct diagnostic entities. And since each disorder suggests different treatment emphases—a focus on pharmacotherapy with possible adjunctive psychotherapy for patients with bipolar disorder versus a focus on psychotherapy with possible adjunctive medication for patients with BPD—making the differential diagnosis is that much more important. Meanwhile, many authors and clinicians have described the diagnostic uncertainty and the challenges in determining if a patient has bipolar disorder or BPD.
The comorbidity: borderpolar
The most frequently researched aspect of the relationship between BPD and bipolar disorder has been the frequency of their co-occurrence. Several reviews have estimated a 20% overlap in diagnostic frequency.3 That is, approximately 20% of patients with bipolar disorder have comorbid BPD and approximately 20% of patients with BPD have bipolar disorder. Thus, while only a minority, there is a meaningful number of patients who are diagnosed with both disorders.
Meanwhile, reviews and commentaries have focused on identifying clinical characteristics that distinguish the two disorders to help with differential diagnosis. This approach implies that the diagnosis is an either/or decision. Framing the discussion as a dichotomous choice underplays the fact that one-fifth of patients have both disorders. The almost exclusive focus on differential diagnosis might discourage clinicians from making both diagnoses, when appropriate, and could result in overlooking an important comorbidity in patients with the greatest need.
Frias, Baltasar, and Birmaher4 recently reviewed the literature on the clinical impact of one disorder on the other. Overall, they found that there have been far more studies comparing patients who have bipolar disorder with and without BPD than there have been of patients with BPD who do and do not have bipolar disorder. Frias et al. found that amongst patients with bipolar disorder, those with comorbid BPD reported more mood episodes, an earlier age of onset of bipolar disorder, greater suicidality, greater hostility, and a higher prevalence of substance abuse. Of note, they found little research examined treatment response, psychosocial functioning, time unemployed, receiving disability payments, or prospectively observed longitudinal course.
The MIDAS project
It has been my clinical experience that patients with both bipolar disorder and BPD (hereafter referred to as borderpolar) are a group at elevated risk for suicide and marked impairment; they also are high utilizers of the most costly levels of care. My colleagues and I recently examined this issue in the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project. We compared psychiatric outpatients with borderpolar to patients with BPD without bipolar disorder and patients with bipolar disorder without BPD. We hypothesized that the borderpolar patients would exhibit significantly more psychosocial morbidity than patients with only one of these disorders.
The Rhode Island MIDAS project represents an integration of research methodology into a community-based outpatient practice affiliated with an academic medical center.5 Psychiatric outpatients presenting for treatment were evaluated with semi-structured interviews. We compared the demographic, family history, and clinical characteristics of three nonoverlapping groups of patients: borderpolar (n=59), BPD without bipolar disorder (n=330), and bipolar disorder without BPD (n=128).
1. Dunner DL. Clinical consequences of under-recognized bipolar spectrum disorder. Bipolar Disord. 2003;5:456-463.
2. Zimmerman M. Borderline personality disorder: a disorder in search of advocacy. J Nerv Ment Dis. 2015;203(1):8-12.
3. Zimmerman M, Morgan TA. The relationship between borderline personality disorder and bipolar disorder. Dialogues Clin Neurosci. 2013;15:79-93.
4. Frias A, Baltasar I, Birmaher B. Comorbidity between bipolar disorder and borderline personality disorder: Prevalence, explanatory theories, and clinical impact. J Affect Disord. 2016;202:210-219.
5. Zimmerman M. Integrating the assessment methods of researchers in routine clinical practice: The Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project. In: First M, ed. Standardized Evaluation in Clinical Practice. Washington, DC: American Psychiatric Publishing, Inc; 2003:29-74.
6. Zimmerman M, Balling C, Dalrymple K, et al. Screening for borderline personality disorder in psychiatric outpatients with major depressive disorder and bipolar disorder. J Clin Psychiatry. 2019;80(1):e1-e6.
7. Frankenburg FR, Zanarini MC. Divalproex sodium treatment of women with borderline personality disorder and bipolar II disorder: a double-blind placebo-controlled pilot study. J Clin Psychiatry. 2002;63:442-446.