Though the two personality disorders share some common symptoms, they are distinct disorders with their own set of diagnostic criteria. For example, both BPD and NPD deal with conflict in a way that is unhealthy to themselves and those around them. It’s the expression of the anger that results from the conflict that is different.
Just like Borderline Personality Disorder, the Diagnostic and Statistical Manual of Mental Disorders (DSM) lists nine symptoms of Narcissistic Personality Disorder. If you exhibit five of these nine symptoms in a persistent manner, you meet the criteria for diagnosis of NPD:
Narcissistic Personality Disorder can exist on its own, but can also be found co-occurring with Borderline Personality Disorder. Mix and match five out of nine symptoms of NPD with five out of the nine symptoms of BPD, and you get someone who will likely be described at least as “difficult” or “high maintenance,” and who certainly is having a tough time in day-to-day life.
Both people with BPD and with NPD deal with an intense fear of abandonment. Enhancing that fear of abandonment is the fact that sustaining relationships with others in the face of these symptoms is a challenge to say the least. “Intense and stormy relationships” is, in fact, one of the characterizing symptoms of BPD.
In an article for Psychology Today, Susan Heitler, PhD, author and Harvard graduate, describes emotionally healthy functioning in the absence of BPD or NPD: “Emotionally healthy functioning is characterized by ability to hear your own concerns, thoughts, and feelings and also to be responsive to others’ concerns.”
In the world of the narcissist, that second part just isn’t present. Narcissists are unable to step outside of themselves to imagine any weight behind someone else’s opinion. This renders someone with NPD socially and emotionally ineffective, and affects their ability to maintain relationships.
The hallmarks of Narcissistic Personality Disorder (NPD) are grandiosity, a lack of empathy for other people, and a need for admiration. People with this condition are frequently described as arrogant, self-centered, manipulative, and demanding. They may also concentrate on grandiose fantasies (e.g. their own success, beauty, brilliance) and may be convinced that they deserve special treatment. These characteristics typically begin in early adulthood and must be consistently evident in multiple contexts, such as at work and in relationships.
People with narcissistic personality disorder believe they are superior or special, and often try to associate with other people they believe are unique or gifted in some way. This association enhances their self-esteem, which is typically quite fragile underneath the surface. Individuals with NPD seek excessive admiration and attention in order to know that others think highly of them. Individuals with narcissistic personality disorder have difficulty tolerating criticism or defeat, and may be left feeling humiliated or empty when they experience an "injury" in the form of criticism or rejection.