Schizophrenia - The diagnosis
So, schizophrenia is not an easy diagnosis to make and not that many people have it (I'll do another post about prevalence, genetics, causes, etc. later).
What I'm about to give you is what's called a differential diagnosis....
Basically, there are 14 or so different diagnoses within the Psychotic Disorder group. To make a diagnosis, one has to combine evidence, critical thinking, and clinical judgment. In short - do a differential diagnosis - by, not only ruling out diagnoses, but also ruling in a diagnosis.
BTW, there is no ONE way to do a differential diagnosis. They key is to be thorough.
That said, what I'm about to give is not thorough. In real life, it takes several sessions with a client, focused clinical interviews, a detailed personal history, and reading over any information released by other agencies, doctors, or therapists.
1. Is there evidence of at least one psychotic episode?
Hallucinations, delusions, disorganization, or negative symptoms? If yes, move on.
If no, then there is no diagnosis of Psychotic Disorder.
2. Were there substances involved when the psychotic symptoms happened?
If it looks like substances (medicine or illicit) were the cause then it's a diagnosis of Substance/Medicine Induced Psychotic Disorder
If substances were involved, but it's not clear they're the cause, stop. To determine if substances were the cause you have to see if there are psychotic symptoms when the client is not under the influence or in withdrawal. This takes time, the client should be clean and sober for a while before ruling out substance-induced psychosis.
If there is no connection with substances or medicine, move on.
3. Does the person have a medical condition which could explain these symptoms?
You're not a medical Dr., so always have someone with suspected psychotic symptoms go see a medical doctor.
If Dr. says "Yep, it's medical condition X.", there's a diagnosis of Psychotic Disorder Due to Another Medical Condition
If Dr. says no medical problem, move on.
4. After ruling out substances and medical conditions, rule out other mental disorders. There are Mood Disorders and at least one Personality Disorder (if not two) that may have psychotic features. So, rule out other mental disorders, Psychotic Disorders are among the last disorders to be ruled-in.
5. Now that you've ruled other things out, look at the client again. Sometimes people only experience one of the psychotic symptoms (sometimes more) for a significant portion of time. If there is at least one symptom present, how long does the episode last?
Between 1 day and 1 month? This yields a diagnosis of Brief Psychotic Disorder
Shorter? Look closely and start back at #1.
6. Sometimes these episodes last longer than one month. So, does the person have at least two of the psychotic symptoms (and at least one of them is delusion, hallucinations, or disorganization) most of the time, from 1 to 6 months?
If yes to 2+ symptoms for 1-6 months, This would be a diagnosis of Schizophreniform Disorder
If mostly catatonia and no hallucinations or delusions, move on to 7.
If mostly delusions, but not really anything else (except maybe related hallucinations), skip to 8.
If all criteria are met for longer than 6 months, skip to 9.
If the criteria isn't met here, then look again at Mood Disorders with Psychotic Features and double-check the diagnoses you ruled out.
7. So, there's catatonia but no hallucinations or delusions?
If there is catatonia, you have to figure out if it is related to another mental disorder, a medical condition, or is "unspecified" (which just means it doesn't fit neatly anywhere else).
If one of those things is the cause, then specify that type of Catatonia
If all those things are ruled out then there is a diagnosis of Catatonia.
8. So, there's delusions and maybe some related hallucinations, but none of the disorganized or negative symptoms?
The diagnosis would likely be for Delusional Disorder
9. Does the person have at least two of the psychotic symptoms (and at least one of them is a delusion, hallucination, or disorganization) most of the time for over 6 months?
If yes, then there may be a diagnosis of Schizophrenia
But...are there any mood/affective elements? If so, keep going...
10. Do the psychotic symptoms co-occur with symptoms similar to depression or mania? Remember back to ruling out Mood Disorders...
If so, maybe no schizophrenia. Maybe there should be a diagnosis of Schizoaffective Disorder
If not, go back to Schizophrenia
Now, there are a few wrenches to throw in here. First, there's a Personality Disorder called Schizotypal which displays some bizarre thinking and behavior as well as interpersonal difficulties. It can be mistaken for Schizophrenia.
And, sometimes a Psychotic Disorder doesn't quite fit any of these categories neatly. We used to then call it Psychotic Disorder Not Otherwise Specified, but now it's divided into Unspecified Schizophrenia Spectrum and Other Psychotic Disorder and Other Specified Schizophrenia Spectrum and Other Psychotic Disorder.
Lastly, I hope it goes without saying that any diagnosis requires that the individual have impairment and/or distress due to these symptoms. And these psychotic symptoms have to be occurring most of the time over the course of a month or so (except in the case of Brief Psychotic Disorder).