-- John H. Watson, "The Adventure of the Red Circle"
Recent years have definitely seen a trend in Sherlockiana, like never before, to diagnose the psychological issues of Mr. Sherlock Holmes. Whether we be amateur of professional, basing our work on scholarly criteria or just comparing him to someone in our lives, the temptation to try to find the pattern to what is going on in that great brain, to unlock just a few of its secrets, is overwhelming. And BBC Sherlock's own Sherlock definitely stimulated that discussion with his own line, right off the bat, "I'm not a psychopath, I'm a high-functioning sociopath." (And even he was making a very amateur assessment.)
One word I've seen come up more than once in connection to Sherlock Holmes's mental state is "narcissist," to which I always want to reply, "Have you met a true narcissist?"
One could argue about a narcissist's lack of empathy or remorse, as Holmes may seem to lack either in some fictional portrayals. In the original Canon, however, one finds both present without much digging. And while Holmes enjoys John Watson's admiration, he does not go out of his way to keep that admiration coming, allowing Watson to make his own judgments about the detective's behavior.
The thing about narcissists, however, that most proves that Sherlock Holmes was not one, is that false reality narcissists create for themselves as the central figure in the universe, bending facts to fit the theories that feed their hungry egos. Sherlock Holmes could not have come close to becoming the world's first and foremost consulting detective if he was not grounded in reality enough to see every truth available. A solid grasp of reality is rather key in that field.
It was important for Holmes to see the world from other people's point of views, to gauge how they might have acted or reacted, to be able to reconstruct scenes that were not in any way something he would have been a participant in. The big blind spot of a true narcissist would not have served Mr. Sherlock Holmes well at all.
It's very tempting to try to do amateur diagnoses of folks around us, and even more tempting to do so with someone who isn't going to walk in the door and prove us wrong at any given moment. And comparing the behaviors of Sherlock Holmes to various conditions, rating how he would fall on a particular scale, can be educational about those conditions. His ephemeral (one hates to use "fictional") nature makes him the perfect brain-dummy to tap with our pointer-stick during a lecture, without anyone getting too upset at our abuses.
In the end, however, I always just want to diagnose him "Sherlock Holmes" and leave it at that.
For when it came to setting the pattern for being a high-functioning Sherlock Holmes, that guy was definitely patient zero.