The Relationship Between Borderline and Bipolar Disorder

Until defining characteristics were established almost 40 years ago in the DSM-III, Borderline Personality Disorder (BPD) was a vague and ambiguous concept. Because a primary characteristic is mood swings, some early researchers insisted BPD was merely a variation of Bipolar Affective Disorder (BAD). After all, if there could be Bipolar I and Bipolar II, why wasn't so-called Borderline Personality Disorder something along the line of Bipolar IV, V, or VI?

Later studies established that prominent symptoms, such as abandonment fears and an unstable sense of identity clearly demarcated BPD from BAD. Genetic data also noted distinctions. A recent Norwegian study¹ employed PET scanning to compare brain functioning in patients diagnosed with BPD, Bipolar II disorder, and a control group.

Researchers discovered similarities and differences in metabolism in these two groups. Both groups, compared to controls, exhibited decreased metabolism in parts of the brain related to emotional control and social interactions. BAD II patients exhibited distinctly decreased metabolism in the cerebellum, brain stem, and parts of the cortex associated in other studies with neurobiological depression. BPD patients showed lower metabolism in other areas including the hypothalamus. The hypothalamus is intimately associated with the endocrine system, which involves stress responses and hormone secretions including cortisol, testosterone, and estrogen. The hypothalamus is also key in the production of oxytocin, which is related to maternal feelings and warm social behavior.

As we learn more about how the brain functions, we must appreciate that symptoms and diagnoses intermingle in various ways. Just as the symptom of a cough may eventually lead to isolation of specific bacteria, diagnosis, and treatment, so a psychiatric symptom may ultimately lead us to isolate a specific region of the brain that leads to a treatment that can relieve suffering.