Personality disorders are diagnoses made from clusters of behaviors, so it’s a different sort of diagnostic category compared to, for example, affective disorders like depression or anxiety. People with personality disorders can be depressed and anxious, but those states tend to come and go pretty quickly, and the overall behavior becomes more salient than the moods.
Personality disorders can be seen as exaggerations or crystallizations of tendencies which can be quite useful in moderation. For example, a little obsessiveness makes us careful and thorough; too much and we have to wash our hands 50 times because there might be a germ we missed. A little suspiciousness helps to protect us from being taken advantage of; too much makes us paranoid. A little narcissism gives us self-confidence; too much and we are all about self-importance. A little flexibility and reactivity can support spontaneity, adaptiveness and creativity; too much and we can have borderline personality disorder.
Here’s the list of characteristics of borderline personality disorder from the DSM-V:
“A pervasive pattern of instability of interpersonal relationships, self-image, and affects, and marked impulsivity, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:
•Frantic efforts to avoid real or imagined abandonment.
•A pattern of unstable and intense interpersonal relationships characterized by alternating between extremes of idealization and devaluation.
•Identity disturbance: markedly and persistently unstable self-image or sense of self.
•Impulsivity in at least two areas that are potentially self-damaging (e.g., spending, sex, substance abuse, reckless driving, binge eating).
•Recurrent suicidal behavior, gestures, or threats, or self-mutilating behavior.
•Affective instability due to a marked reactivity of mood (e.g., intense episodic dysphoria [distress, unease], irritability, or anxiety usually lasting a few hours and only rarely more than a few days).
•Chronic feelings of emptiness.
•Inappropriate, intense anger or difficulty controlling anger.
•Transient, stress-related paranoid ideation or severe dissociative symptoms.”
Personality disorders, like most mental disorders, occur along a spectrum of intensity and severity. Some people have a “borderline style,” are borderline-ish or have borderline tendencies, while others may have the full-blown disorder; and of course stress can push a tendency or style into a disorder.
People with borderline personality styles or disorder often improve from the late 20s through the 30s and into their 40s, which is when the prefrontal cortex undergoes adult maturation. That tends to be the time when therapy can be most useful, probably because the person is more able to do self-observation, and exercise inhibition of impulsivity, two executive functions associated with the prefrontal cortex. It seems likely that there’s some relationship between an immature prefrontal cortex and other parts of the brain involved in borderline personality; although we can only speculate, for the time being, about what that might be.
Just because people have the same diagnosis doesn’t mean that they are the same kinds of people. There can be variations in how likable and personable, generous or mean-spirited, humorous or dour, and even wise, people with borderline personality disorder can be. This is true of any mental illness; for example, everyone with depression isn’t alike.
Because of the tendency to see others in a black-and-white, caring/helpful or hating/destructive way, people with more extreme borderline personality disorder tend to split people in organizations into supporters and opponents. Inpatient or residential mental health programs typically will inform staff if a borderline patient is admitted so that staff will use extra care to check on all communications that might have the effect of pitting one staff member against another. The ability, on the part of the person with borderline personality style or disorder, to see other people in their human complexity rather than in black-and-white, good-and-bad terms, is a sign that the person is healing or maturing.