The detail of the highest-ranking therapist, plus others -the need for validation, the fact that the writer declares to be keen on interpersonal connections, the general air of self-involvement, plus the simple act of dishing personal stuff in public - makes me think more of narcissism than psychopathy.

(IANA psychiatrist, needless to say)

In fact, I suspect that most people who flaunt their psychopathy on the internet are in fact narcissists. The two psychos I've met in my life couldn't have cared less for attention from the public at large or validation of their struggles. I can't really imagine them writing an open letter about their condition, an act that doesn't provide tangible control, or money, nor damages an enemy. On the other hand, narcissists needs validation and attention and writing an open letter is attention-seeking behaviour (which we are involuntarily feeding).

Could he perhaps be both?

It's totally possible. I think comorbidity it's called 'malignant narcissism'.

You might not be all that far off the mark. I'd imagine people who fall somewhere within the dark triad [1] would connect better with a psychopath, even if they are not one themselves.

[1] http://en.wikipedia.org/wiki/Dark_triad