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.
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 report an estimated 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 with a comorbid diagnosis.
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 can result in overlooking an important comorbidity in patients with the greatest need.
Frias and colleagues4 reviewed the literature on the clinical impact of one disorder on the other. Overall, they found that there have been far more studies that compared 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. The researchers also noticed 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 that examined treatment response, psychosocial functioning, time unemployed, 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).
The results showed that significantly more patients with borderpolar had diagnoses of three or more Axis I disorders than patients with bipolar disorder. Borderpolar patients also reported significantly more PTSD, obsessive-compulsive disorder (OCD), substance use disorder, and somatoform disorder compared with the patients with bipolar disorder. Similarly, patients with borderpolar reported significantly more OCD than patients with BPD.
In terms of risk factors, the MIDAS study found that borderpolar patients had the most psychopathology in their first-degree relatives. Compared with patients with bipolar disorder, the morbid risk for depression, bipolar disorder, PTSD, specific phobia, drug and alcohol use disorders was significantly higher in the borderpolar patients. Compared with patients with BPD, borderpolar patients had significantly higher morbid risks for bipolar disorder, PTSD, and drug and alcohol use disorder.
Furthermore, psychosocial morbidity was greatest in the borderpolar patients. Compared with bipolar disorder patients, the borderpolar patients reported more episodes of depression, more anger, suicidal ideation, history of suicide attempts, childhood trauma, chronic and persistent unemployment, impaired social functioning, and psychiatric hospitalizations. These patients were also more likely to receive disability payments and they exhibited significantly more psychosocial morbidity than the patients with BPD. The borderpolar patients reported more episodes of depression, childhood trauma, chronic and persistent unemployment, history of suicide attempts, and psychiatric hospitalizations.
The results from the MIDAS project indicate that patients with both bipolar disorder and BPD are more severely ill than patients with only one of these disorders. While clinicians might seek diagnostic parsimony and diagnose only one disorder, it is important that they not overlook the potential presence of the other disorder.
During the past decade, significant effort has been put forth to improve the recognition of bipolar disorder in depressed patients. Several screening scales for bipolar disorder have been developed, and they have been extensively researched. Similarly, peer reviewed journals have published review articles and commentaries about the importance of recognizing bipolar disorder in patients presenting for treatment of depression. Much less has been written about the importance of improving the recognition of BPD. Just as it is important for clinicians to include questions to screen for a history of manic or hypomanic episodes in their evaluation of depressed patients, it is important to screen for the presence of BPD in patients with mood disorders.6
To date, practically no research has examined potential treatments for patients with both diagnoses. There are only a small number of open-label trials of medication, one controlled medication trial, and no controlled psychotherapy trials of patients with both disorders.7
While the literature has clearly demonstrated that bipolar disorder and BPD are distinct disorders, the importance of diagnosing both disorders when comorbid has gotten lost in the dialogue. It is our hope that by giving this group of severely ill patients a unique name-borderpolar-the recognition of this comorbidity will increase. And, as such, there will be increased efforts to identify the most effective treatment approaches.
The ongoing debate as to whether BPD belongs on the bipolar spectrum, which has generated a robust empirical data base establishing that these are distinct diagnostic entities, has sidetracked researchers and clinicians from recognizing the importance of diagnosing both disorders when both are present. Patients with comorbid bipolar disorder and BPD (ie, borderpolar) represent a group with severe psychosocial morbidity who are often unemployed, suicidal, and utilize more costly forms of health care services. Efforts to identify effective approaches towards treating these patients have been minimal and are needed.
This article was originally published on 10/4/19 and has since been updated.
Dr Zimmerman is Professor of Psychiatry and Human Behavior at The Warren Alpert Medical School of Brown University and Director, Partial Hospital Program and Adult Outpatient Psychiatry at Lifespan. He presented “Borderpolar: Diagnosis and Treatment of Patients With Bipolar Disorder and Borderline Personality Disorder”at the 2019 Psych Congress in San Diego, CA.
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