Borderline personality disorder and bipolar disorder share some features ( mood changes for example). This sometimes make it difficult to differentiate shades of bipolarity with personality disorder. Patients increasingly prefer to have a diagnosis of bipolar disorder rather than the other. An invited comment by Barroilhet et al briefly describes the differences between the conditions that is really central in making the distinction.
1. Psychomotor activation is central to bipolar disorder. This manifest as decreased need for sleep, increased energy, increased goal-directed activities and pressured speech.Most impulsive acts in the manic or hypomanic phase could be understood as goal directed activities.Pure impulsive behaviour as such is less of a problem in mania.
2. Self destructive cutting is common and often central in borderline disorder.Highly uncommon in bipolar disorder
3. Bipolar disorder is highly genetic in origin. Borderline personality disorder is highly associated with sexual trauma.
4.Bipolar is an episodic disorder. Personality disorder is a chronic and constant condition.
5. Fear of abandonment, identity disturbance, recurrent suicidal or self-mutilating behavior, and dissociative symptoms are central to diagnosis of borderline personality disorder. These are highly unlikely to be seen in bipolar disorder.
Comment: Clinically, there will be patients where this differentiation can be difficult. For example, mood instability in inter episode period in bipolar disorder can create difficulty in an occasional patient.Sexual trauma is more common in bipolar disorder than general population. There would also be situations where both disorders can be diagnosed at the same time, making it difficult to ascertain where each symptoms belong.The idea of bipolar spectrum disorders have encouraged clinicians and patients to at least consider whether other disorders with mood instability and impulsivity ( like ADHD and Borderline PD) are manifestations of bipolar disorder.One could argue that it is a positive step as long as the distinction is clearly made.
Summary of the article:
Barroilhet S, Vöhringer PA, Ghaemi SN. Acta Psychiatr Scand. 2013 Nov;128(5):385-6.