I was intrigued by the observation that high levels of narcissism tend to be associated with an increase in "flip-flopping" between grandiosity and self-doubt/vulnerability, e.g as stated in Jauk et al. (2017):
Specifically, clinical observations show that patients diagnosed with narcissistic personality disorder (NPD), a pathological form of narcissism, display co-occurring or oscillating states of grandiosity and vulnerability (Pincus and Lukowitsky, 2010). Recent systematical investigations confirm that this is particularly true for individuals identified as grandiose narcissists, who display episodes of vulnerability (Gore and Widiger, 2016).
This made me try to draw a parallel with bipolar disorder. Alas it doesn't look like the relationship has been studied much with respect to bipolarity as the core feature. What I mean by that is that I found a paper contrasting mania with (mostly grandiose) narcissism:
As hypothesized, tendencies toward both narcissism and hypomania related to elevations on measures of affective and goal dysregulation. In addition, hypomania tendencies were related to higher impulsivity, but that association did not appear for narcissistic tendencies.
Buy maybe I've missed some relevant literature in my quick search. So is there more to be said about bipolar disorder and narcissism, beyond the correlation that mania draws with grandiosity?