If you go back far enough, autism wasn't distinguished from schizophrenia: https://en.wikipedia.org/wiki/History_of_autism https://en.wikipedia.org/wiki/Histor

If you go back far enough, autism wasn't distinguished from schizophrenia: https://en.wikipedia.org/wiki/History_of_autism https://en.wikipedia.org/wiki/History_of_autism > Eugen Bleuler was a Swiss psychiatrist who was the director of the Burghölzli mental hospital, which was associated with the University of Zurich. > In April 1908 he gave a lecture explaining that dementia praecox was very different to other forms of dementia.[34] He proposed that it be given the unique name schizophrenia - a split mind. The term would be increasingly adopted over the next fifty years. > What is now known as "schizophrenia" is different from what Bleuler described. He included what is today considered as autism, schizoid personality disorder and various schizophrenia spectrum disorders in his definition. > The Neo-Latin word autismus (English translation autism) was coined by Blueuler in July 1910.[35] He first used it in print to describe a symptom of schizophrenia in the scientific paper "Zur Theorie des schizophrenen Negativismus"[36] (On the theory of schizophrenic negativism). He derived autismus from the Greek word: αὐτός, romanized: autós, lit. 'self', and used it to mean morbid self-admiration, referring to "autistic withdrawal of the patient to his fantasies, against which any influence from outside becomes an intolerable disturbance".[35][36] > Bleuler created the term in reference to Sigmund Freud's term autoerotismus, shortening the latter term because he did not believe sexuality to be critical in the etiology of autistic symptoms.[36] He characterized the autistic patient as one who "wants to shut himself off from reality".[36] Autistic people, then, are those "most severe schizophrenics, who no longer have any intercourse at all, live in a world of their own".[37] > Bleuler believed that the idiosyncratic behaviours of people with schizophrenia displaying autistic behaviour were due to them engaging with personal fantasy rather than with the world as it is.[1] He believed they drew on an early childhood mental state that was unable to form theory of mind.[1] Point being, trying to track the incidence of mental and neurological disorders through history is even more difficult than most would imagine.