The characteristics of this disorder fit him better than “high functioning sociopath” or “Asperger’s”.
Schizoid PD can explain his emotional "coldness", lack of sexual interest, disregard for social norms and why he hardly notices when John leaves the flat.
This Might Explain a lot
Schizoid personality disorder has nothing to do with schizophrenia. Schizoid is supposed to mean “like schizophrenia” because there is blunting of displays of emotion in both conditions but they are not related disorders.
Schizoid PD is also not to be confused with schizotypal PD which is characterized by preferred isolation, anxiety in social situations, odd thoughts and unconventional beliefs.
People who are schizoid have certain characteristics that on the face of it would describe Sherlock Holmes very well:
In the World Health Organization's ICD-10 diagnostic manual: schizoid personality disorder is characterized by at least four of the following criteria:
Emotional coldness, detachment or reduced affect – This criterion doesn’t require the patient to have a lack of empathy or in more colloquial terms “be heartless”. It refers how emotions are displayed rather than the absolute presence of any emotion. Although this can be social subjective (i.e. different in more reserved cultures) I think Sherlock ticks this box.
Limited capacity to express either positive or negative emotions towards others – Sherlock is quite able to express his negative emotions towards others in very loud terms.
Consistent preference for solitary activities – crime solving for Sherlock was a very solitary activity. He works alongside others like Lestrade but most of his activities were solitary until John came along. Sherlock was the one to convince John to join him, and prefers to work with John hence why he doesn’t tick this box.
Very few, if any, close friends or relationships, and a lack of desire for such – Sherlock definitely has few friends – as Mycroft mockingly says quite a number of times. However it appears that Sherlock does have a genuine desire for close relationships at least with John.
Indifference to either praise or criticism – He thrives on attention and praise, and is on occasion put out by John’s criticism.
Taking pleasure in few, if any, activities – Sherlock really only enjoys crime-solving, when he doesn’t have a case he becomes insufferable because he finds neither pleasure or simulation in other activities.
Indifference to social norms and conventions – Sherlock definitely fulfills this criteria. He understands what the social norms are, he just couldn't care less.
Preoccupation with fantasy and introspection – fantasy in this sense does not mean Dungeons and Dragons. Fantasy refers to the use of imagination to construct imaginary scenarios. These can be fantastical or purely mundane. When Sherlock works out scenarios inside his head, he must use his imagination to fantasize/visualize in a logical manner about the various possibilities. Patients who fulfill this criteria often describe a vivid, rich and interestingly well organised internal world inside their head, which they understandably prefer to outside world. Sherlock is quite typical of this kind of patient. He retreats inside his own head on several occasions, so much so he fails to notice when John leaves the flat.
There’s at least three criteria that fully apply and two that partially apply to Sherlock. It is important to bear in mind that very few people will ever tick all nine boxes because manifestations of schizoid are very varied. The nine criteria are there to try and catch all the different possible subtypes.
Some psychiatrists would be happy to diagnose Sherlock, others would be more cautious and record that he has schizoid traits.
And then Some More…
Other characteristics that are often seen in people with schizoid personality disorder but don’t appear on the diagnostic criteria are: narcissism and a sense of superiority, as well as loneliness.
Patients with schizoid PD do tell psychiatrists that they feel extremely lonely but not so many of them express a concrete wish for meaningful relationships. At times when interviewing such patients I get the feeling that they do not make the full emotional connection between loneliness and lack of relationships.
Unlike in many other personality disorders people with schizoid PD can have very good insight into their disorder. They often realise that they are different, and they can even pinpoint the specific parts of their personality that cause problems. What they are not always able to articulate is why they behave in the way they do or how their lives can be improved.
Very few patients I’ve seen are quite as flamboyant as Sherlock but then there are many different subtypes of schizoid. Schizoid PD is not so much one discrete disorder, as a varying spectrum of similar disorders that all tend to overlap with each. Sherlock symptoms predominantly revolve around detachment, elaborate internal world and narcissism. There are many depressive, avoidant and disassociative features of the disorder that he doesn't display.
The differential diagnosis for patients who show schizoid traits includes Asperger’s Syndrome in adults. The most obvious manifestations of schizoid can be mistaken for Asperger’s Syndrome particularly blunt affect (can be mistaken for lack of displays of empathy), consistent preference for solitary activities and problems with interpersonal relationships to name but a few.
I think this might be what makes many people so convinced Sherlock has Asperger’s. It is unlikely that Sherlock has Asperger's Syndrome (Sherlock, Himself and His Aspergers) but obviously not impossible. He does not fulfill enough of the criteria for Asperger's to be diagnosed in any case. Schizoid personality disorder is for Sherlock a more appropriate diagnosis because the symptoms overall fit more closely with the man that we see but it does not exclude other psychiatric conditions.
Schizoid has a higher prevalence in families where one member has schizophrenia. I wonder if perhaps one of the Holmes parents had schizophrenia. It may be very difficult to bond with or have a consistent relationship with a family member (particularly a parent) who has poorly treated schizophrenia. Some psychiatrists believe that this emotional inconsistency is the early damaging trigger for the development of schizoid personality disorder. Others have pointed out that children of schizophrenics are more likely to develop many other psychiatric disorders - including depression, anxiety and of course schizophrenia. The correlation between schizoid and schizophrenia may not be particularly significant.
I personally don’t think Sherlock would be diagnosed with schizoid personality disorder, mostly because he would never agree to see a psychiatrist, but also because much of Sherlock's symptoms may be attributed to other psychological issues (Explaining Sherlock's Sherlockness).
Besides, Sherlock will not benefit from a psychiatric diagnosis of any kind, he is clearly happy the way he is. Everyone has maladjustments - as one psychiatrist puts it: "the only people who aren't afraid that they might be crazy, are the people who are already crazy."
I just think Sherlock should just start calling himself “a high-functioning schizoid” instead (not that high functioning can be applied to personality disorders) that would really confuse Anderson.