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Your son appears to be suffering from Delusional Disorder, Persecutory Type. This is the most common variety.
Delusional order is a lot less common than Schizophrenia, and usually does not lead to it. As you noted, correctly, the lack of hallucinations and the nonbizarre thinking lead diagnosis away from schizophrenia. HIs relatively late onset (age 19) is also typical of Delusional Disorder.
He has certainly been given a shopping list of pharmaceuticals, which is one approach that is used.
There may be other reasons for his delusional thinking. Let me mention them briefly:
- Central nervous system disorders, including tumors and seizure disorders
- Vascular disease
- infectious diseases
- Metabolic disorders
- Vitamin deficiencies
- Medication reactions
- Drug use (pot, meth, coke, etc)
Somatic delusions seem more responsive to antipsychotic therapy than other types of delusions (regardless of whether this treatment was pimozide or other antipsychotics). However, this apparent difference may mostly result from the generally poor response rates for delusional disorder with persecutory delusions (50% improvement rates, with no reports of complete recovery).
If he has not been thoroughly checked out medically, then do so as you may discover other factors. Genetics are also important, as this can be inherited.
If I have helped and shed some more light on your situation, please accept my answer so that I may continue the important work of helping others in need and pain.
Great blessings to you family.
Elliott Sewell, LPCC, NCC