Distinguishing Borderline From Bipolar Spectrum Disorders

Key points:

• Accurate diagnosis of borderline and bipolar conditions is essential.

• Borderline personality disorder is marked by primitive defenses and interpersonal hypersensitivity.

• Mood shifts in borderline personality are reactive; in bipolar disorder, they’re cyclical.

How do we distinguish between bipolar mood disorder, cyclothymic temperament, and borderline personality disorder? This may be among the most important questions in clinical psychiatry and psychotherapy.

The ability to accurately distinguish between these conditions frequently leads to treatment success; misdiagnosis can result in major failures. For instance, bipolar disorder is often well-treated with medication. Lithium therapy can lead to remission of symptoms and prevention of future episodes in appropriately selected patients (Ghaemi, 2024). In contrast, medication does not treat the core symptoms of borderline personality disorder. Misdiagnosis of borderline personality disorder as a mood disorder often results in multiple failed medication trials and prolonged suffering and impairment.

Much diagnostic confusion results from significant symptomatic overlap, particularly in the area of mood symptomatology.

Below are two fundamental features of borderline personality disorder that are not present in bipolar spectrum disorders. I teach psychiatry residents to use these pointers to help differentiate the two forms of psychopathology. They are:

1. Borderline personality disorder is marked by a reliance on primitive defense mechanisms: splitting, projection, and projective identification (Kernberg, 1975).

These defenses pervade the lives of borderline patients. For instance, splitting refers to the tendency to see self and others as being either "all good" or "all bad," with an inability to see things in "shades of gray." This symptom is captured by DSM-5 criteria for borderline personality disorder ("…alternating between extremes of idealization and devaluation") (American Psychiatric Association, 2013). We do not see this as a prominent symptom in bipolar disorders.

2. Borderline personality disorder is marked by the patient's fundamental interpersonal hypersensitivity (Gunderson & Lyons-Ruth, 2008).

Symptoms of borderline personality disorder are mediated by the patient's subjective experience of the major object (sometimes referred to as the patient's "favorite person"). This was Gunderson's (1984) seminal contribution to understanding borderline psychopathology. He wrote, for instance, that "these characteristic disturbances in interpersonal relations uniformly provide the most distinguishing aspect of the borderline syndrome vis-à-vis a variety of other diagnoses" (Gunderson, 1984).

Contrary to Linehan's (1993) claim that emotional dysregulation represents the "core" of borderline personality disorder, mood problems in borderline patients are actually secondary to interpersonal hypersensitivity, which is the "engine" that drives all borderline symptoms.

Patients with borderline personality disorder are prone to abandonment depression, which Masterson (2000) saw as the primary affective state in the borderline personality. For instance, a person with borderline personality disorder may experience feelings of depression, emptiness, and suicidal despair in response to a minor or imagined distancing by their romantic partner. These symptoms can easily be misdiagnosed as a major mood disorder.

Mood symptoms are actually a very poor discriminating feature, and this is the source of much confusion, misdiagnosis, and mistreatment (Ghaemi, 2014). Both borderline personality disorder and bipolar spectrum disorders can present with intense affective shifts, but in borderline patients, these shifts are reactive to interpersonal events rather than driven by endogenous mood cycling.

In addition, individuals with cyclothymic temperament exhibit chronic, low-grade mood instability that fluctuates independently of relational dynamics and lacks the identity diffusion, primitive defenses, and object-related dysregulation characteristic of borderline personality disorder.

The differential diagnosis of these problems becomes much easier if one keeps these two points in mind.

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