Bipolar and Borderline: A Differential Roadmap

Understanding the differences improves diagnosis and treatment.

Posted May 28, 2020

The essential problem in assessing bipolar disorder with other mental disorders is the lack of a clear roadmap for an accurate differential diagnosis. As I have written before, nearly two-thirds of people with bipolar have been misdiagnosed at least one time in their lives and will have consulted an average of nearly four professionals before receiving the proper bipolar diagnosis. What is perhaps most disturbing is the length of time it takes for an individual to receive a bipolar diagnosis and appropriate treatment. The average time from when a person experiences the first bipolar mood episode to receiving treatment specifically for bipolar disorder is about 10 years. This gap in treatment is the result of a profound misunderstanding of what bipolar is, how it presents itself in episodes that can come and go, and a general reticence to discuss having a chronic mental illness, especially when symptoms are present in a young person.

While most people with bipolar disorder are diagnosed with non-bipolar major depression, many are inaccurately diagnosed with a personality disorder. It is true that someone with bipolar disorder can also have a co-occurring personality disorder, but these classifications can often be confused for each other and create treatment complications as a result.

Some personality disorders can mimic the behavioral signs within bipolar mood swings, especially in the manic mood zones. Borderline, narcissistic, and antisocial personality disorders can have some of the closest similarities to the more salient aspects of bipolar disorder. In this post, I’ll focus specifically on borderline personality disorder and how to better differentiate it from bipolar disorder.

Borderline individuals typically display stark emotional changes, turbulent relationship patterns, and irresponsible or risky personal behaviors. A key component of borderline personality is called idealization/devaluation, or splitting. This means a borderline person can idealize another person in a relationship (including a therapist during the course of therapy) as “all good” or a “perfect soul mate.” Later, and usually without apparent provocation, that same amazing person will be devalued by the person with the borderline condition as “all bad” or “useless.” This drastic shift in cognition, emotion, and behavior towards others is a hallmark of borderline personality.

But the harsh instabilities in mood, relationships, and social behavior can appear manic, and thus easily be confused with bipolar disorder. Any differentiation between the two disorders is complicated by the fact that those with borderline personality disorder can suffer severe depression with suicidal thoughts and actions in the same way people with bipolar can. But while the instability of mood is a persistent problem with borderline personality, in bipolar, mood changes come and go with periods of baseline stability. People with borderline personality also intensely fear abandonment in relationships, which certainly can happen in people with bipolar, but is not itself a feature of bipolar disorder.

The first major distinction between these diagnoses is that bipolar is a primary disorder of mood and borderline is a primary disorder of personality involving longstanding interpersonal dysfunction. As a result, bipolar disorder manifests in mood episodes that can change rapidly or in long stretches, with periods of ostensible balance in between, referred to as the baseline mood zone. Therefore, symptoms of bipolar disorder are regarded as episodic. Conversely, borderline personality is considered pervasive, where symptoms and functional consequences of the disorder are continual across mood states. This may seem deceiving to some who have seen people with borderline appear to be happy, mellow, or just having a “good day,” as a bipolar-type baseline mood zone. But while immediate behavioral signs may point to a stable mood position, the pervasiveness of borderline personality often reflects an ongoing entangled and chaotic mess of interpersonal relationships and self-image no matter what mood state is present.

So, while mood instability and interpersonal conflicts can be salient in both bipolar and borderline, the differences begin in the origins of symptoms and their behavioral consequences. One way to approach this is to ask the question, “What primary aspect of the particular disorder is driving the secondary product?” Bipolar disorder is a disorder of mood, which originates genetically and affects the brain’s ability to regulate emotion. In effect, the bipolar mood swings drive consequences in the person with the disorder, including increased impulsivity and interpersonal disruptions.

Mood lability in borderline personality disorder may be more reactive and subsequent to the internal and interpersonal turmoil driven by the profound underlying fear of abandonment, along with intense feelings of emptiness and alienation. While these factors don’t entirely preclude borderline as having some kind of genetic association, psychosocial and psycho-developmental factors appear to dominate the borderline etiology. In fact, the fear of abandonment so permeates borderline behavior that it can essentially govern every shift in mood and action, as we can see in the ego defense of splitting, which reduces others to objects easily divided into idealized and devalued parts. The essential goal of splitting is to both fill the sense of emptiness through idealizing and over-identifying with the other (or object), while controlling the anxiety of the perceived inevitable abandonment by means of devaluing the other, oftentimes with considerable hostility.

Stress and anxiety, including the fear of abandonment, can certainly influence a mood episode in bipolar disorder. However, this would be more of a catalyst to the foundational and pre-disposed nature of neurological changes that govern mood episodes and would be only one of potentially several catalysts, including those of both endogenous and exogenous origins. Anxiety in someone with borderline personality, and the responses to it including self-harm, suicidal gestures, erratic spending, hypersexuality, or outbursts of rage stem from underlying fear in the context of interpersonal and ego dysfunction. And as splitting is a primary ego defense in borderline personality, denial appears to be a far more predominant defense in bipolar disorder. In fact, if splitting is persistent in someone with a clear diagnosis of bipolar disorder, there is a reasonable likelihood that borderline personality coexists with the overall bipolar condition.

Another factor that can be useful in separating these diagnoses involves onset. The average age of bipolar onset is 18 years of age, which means that children can show signs of the disorder early in life, and perhaps may have expressed prodromal symptoms prior to a complete constellation of symptoms that meet DSM-5 criteria in adult life. There is no average age of borderline onset per se; in fact, the longstanding nature of this disorder of character means that a diagnosis requires active and persistent symptoms well into adult life. Certainly, some adolescents can demonstrate borderline traits that may eventually coalesce into a borderline diagnosis, but this is not in itself a reliable predictor for the diagnosis in later life. Mood instability in bipolar disorder, however, can often be traced to childhood, especially if noticeably triggered by adolescent hormonal changes and does not stabilize into early adulthood.

The overlap of bipolar and borderline symptoms may seem to suggest that treatment approaches would be similar, but this is not typically the case. While I believe that both disorders need protracted psychotherapy services, especially in the individual modality, there are some important differences to consider. In bipolar, therapy is focused in the pre-stabilization phase on the immediate crisis created or exacerbated by bipolar mood swings, working through denial towards acceptance of the bipolar reality, and any intrapsychic conflicts related to the initiation of bipolar medication trials towards mood stabilization. In borderline personality, establishing trust in the therapeutic alliance is often the top priority, especially given the individual’s pattern of interpersonal instability. Not that people with bipolar don’t need a solid experience of trust in therapy to move forward; but with borderline patients, establishing and maintaining trust and constancy in a therapeutic alliance is paramount to any reasonable prognosis in improving self-image, frustration tolerance, and interpersonal functioning. And even then, therapy may take many months or years of consistent therapy before such improvements are sustainable.

As someone with bipolar disorder progresses through stabilization towards post-stabilization, therapy can focus increasingly on the prior functional consequences of the disorder (e.g., financial distress, extramarital affairs, drug abuse, etc). This progression can make therapy more broadly effective with respect to related life issues and allow for other treatment modalities, such as couples therapy, to be more adaptable to particular life conflicts. In therapy for borderline personality, the increased sense of reliance on the therapist as a trusted figure often reignites profound fears of abandonment, which promote ego defenses, paranoid projections, and the unconscious reenactment of psychological trauma, all of which can reoccur throughout treatment. A therapist treating a patient with borderline personality should anticipate and prepare for these features as they become manifest in the transference phenomenon.

Another reason to differentiate bipolar and borderline involves medication issues. Mood stabilizing medications, such as lamotrigine, are generally effective for bipolar disorder but have not shown to be consistently effective in borderline personality disorder. It’s understandable, though, why a treating physician might prescribe a mood stabilizer over an antidepressant, especially if he or she is concerned about an underlying bipolar disorder in someone with a primary presentation of borderline personality. That’s because antidepressants, such as SSRIs and SNRIs, can act as catalysts for mania in people with bipolar disorder, especially if no mood stabilizer is present in the regimen.

Doctors may also consider atypical antipsychotic medication if there is no clear differentiation of borderline and bipolar symptoms, especially if evidence of psychosis is suspected. While it may be true that the pharmacological treatment of borderline personality is generally more complicated than that of bipolar disorder, a clearer diagnostic picture can assist physicians in opening a wider array of treatment options for these disorders, whether they may be distinct or co-occurring.


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