Narcissistic Personality Disorder is part of a wider continuum of narcissism not the sum total of it all. NPD is not the sole domain of narcissism. Narcissism, to varying degrees, is also a part of Borderline Personality Disorder (BPD). Narcissism is a primitive defense mechanism common to both personality disorders though not manifested exactly the same and not serving the exact same purpose always. Narcissism in BPD is not as extreme as it is in NPD. However, that distinction made there are many people who are diagnosed with both personality disorders. Both NPD and BPD can co-exist within an individual.
