Psychosis: Differential diagnosis
Ruling out underlying organic pathology
Many medical illnesses can cause psychotic symptoms, but they generally have other symptoms and signs associated with the primary disease.
For first presentations of psychosis, a physical examination that includes a neurological examination, general medical history and review of symptoms should be conducted. Unless otherwise indicated by the history or physical examination, screening blood tests should include complete blood count, blood chemistry including electrolytes, liver function tests and a thyroid-stimulating hormone test.
For these first-time patients, a CT or MRI is recommended to rule out structural brain abnormalities.
Ruling out other pathology
In addition to ruling out organic pathology, investigate:
- delirium or dementia
- substance intoxication or withdrawal. A toxicology screen is also recommended because substance intoxication and withdrawal can present with psychotic symptoms.
- mood disorder with psychotic features (depression or mania). Mood disorder with psychotic features can be differentiated from schizophrenia by the exclusive appearance of psychotic symptoms during periods of mood disturbance.
Identifying the specific psychotic disorder
Brief psychotic disorder
Brief psychotic disorder is characterized by psychotic symptoms lasting
at least one day but less than one month.
Schizophreniform disorder is characterized by symptoms of schizophrenia that last at least one month but less than six months.
Delusional disorder is characterized by non-bizarre delusions and the
absence of other characteristic symptoms of schizophrenia (e.g., hallucinations, negative symptoms, disorganized speech or behaviour).
Schizoaffective disorder is characterized by a mood episode that is concurrent with psychotic symptoms of schizophrenia, where the mood symptoms are present for a substantial portion of the total duration of the disturbance, and psychotic symptoms must also be present for at least two weeks in the absence of prominent mood symptoms.
Schizophrenia is characterized by the presence of symptoms (e.g., hallucinations, delusions, negative symptoms, disorganized speech or behaviour) for at least six months (see summary of DSM-5 diagnostic criteria)