Actually I'm not meaning to talk about Kohut's theory though the terms may have originated with him - I'm meaning to be talking about the conceptualization that is accepted by the current diagnostic authority - The american psychaitric association.

Narcissistic personality disorder and borderline personality disorder are both considered to be instances of the same 'cluster' of personality disorders.

You will find the idea that narcissism is a defense against low self esteem in a number of places. Also comes up with respect to mania being a defense against depression / despair and grandious and paranoid delusions particularly so.