Also there's huge overlap in symptoms between bipolar I with psychosis, schizoaffective disorder, and schizophrenia. People sometimes move around between these diagnoses throughout treatment, different doctors have different opinions, patient behavior changes, etc.
I personally think these symptoms come about through many different causes and the labels are somewhat inadequate. They capture a symptom profile rather than a full understanding.
I remember reading in Courtenay Harding's (now very old) book, Recovery from Schizophrenia: Evidence, History, and Hope, that populations with a higher prevalence of bipolar tended to have a lower prevalence of schizophrenia, and vice versa. The implication was that the same thing was being expressed differently in differing contexts. I would be curious if more contemporary studies bore this out.
The overlap is not huge at all. Beside psychosis, they have no overlap, and the quality of the psychosis in the two illnesses is far removed from each other.
I'm speaking about people I've known and been close to. As an example, my brother shifted around diagnosis between bipolar I, schizoaffective, and schizophrenia often while I was growing up. He's not the only person I know like this. I've spoken to psychiatrists about the ambiguity between these diagnoses.
I also know of numerous people who have spoken publicly about receiving a schizophrenia diagnosis and having it later be revised to schizoaffective disorder.
I also came to the impression that it is common to receive a bipolar I diagnosis during a psychotic episode and have it later the diagnosed as schizophrenia or schizoaffective disorder.
Sometimes if your doctor sucks you may stay in the less accurate diagnosis, sometimes for years.
Same in someone I know, shifted between bipolar and schitzoaffective and schitzophrenia. Bipolar during manic episode, later schizoaffective. A lot of paranoia and also delusions, but also refused medication due to side effects (and probably the disorder itself).
I'm a non expert but I believe some people are starting to see it that way. See: https://www.google.com/search?q=schizophrenia+spectrum+disor...
Also there's huge overlap in symptoms between bipolar I with psychosis, schizoaffective disorder, and schizophrenia. People sometimes move around between these diagnoses throughout treatment, different doctors have different opinions, patient behavior changes, etc.
I personally think these symptoms come about through many different causes and the labels are somewhat inadequate. They capture a symptom profile rather than a full understanding.