The diagnostic criteria for schizophrenia specifically excludes an identifiable medical source of symptoms. That’s not to say your character can’t exhibit some schizophrenia-like symptoms, just that they would not receive the diagnosis of schizophrenia.
The relevant diagnosis would actually be “Psychotic disorder due to another medical condition”, which is a bit different from schizophrenia.
I’ll do a quick Demystifying the DSM 5 breakdown of the criteria!
Psychotic disorder due to another medical condition
- Prominent hallucinations or delusions
- There needs to be evidence (either from the patient’s medical history, physical examinations, or lab tests) that these symptoms are directly caused by a medical condition.
- It’s not better explained by another mental disorder.
- It’s not just part of a delirium (see here).
- These symptoms cause the character significant stress and/or make their life more difficult.
The actual diagnosis needs to follow the following formatting:
“Psychotic disorder due to [[insert medical condition here]] with [[whichever symptom is more dominant, delusions or hallucinations]]”.
You’ll notice that some of the symptoms of schizophrenia are missing from this. That’s because these other symptoms are really uncommon when a medical condition is causing psychosis.
There are some other things you should note specifically for Psychotic disorder due to traumatic brain injury:
- There’s a specific type of brain injury that has been found to cause psychosis (lesions to the frontal and temporal lobes).
- The psychosis tends not to show up immediately following the TBI; there’s usually a significant delay (we’re talking anywhere from months afterwards to 5-10 years afterwards).
- Despite negative symptoms being extremely uncommon when psychosis is caused by a medical condition, when we’re talking specifically about TBIs, the symptoms may look a bit more like schizophrenia. About 37% will show negative symptoms.
- The most common symptoms are:
- Delusions (92%) – most commonly persecutory delusions
- Hallucinations (87%) – most commonly auditory
- Psychosis is not going to be the only symptom of the TBI. It’s also associated with seizures and highly comorbid with cognitive impairments in memory and executive functioning.
- The majority of people with this disorder find their psychosis improves when treated with antipsychotics.
As for your second question, it depends. I can go into that in another post; this one is pretty long already!