How likely is it for someone to develop schizophrenia as the result of a TBI without having the genetic predisposition. Also, if a person thinks they are being possesed by some spirit, entity etc, is that considered dissociation, delusion, or something else? Thank you.

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!


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