The diagnosis of a delusional disorder is made when a person has one or more non-bizarre (situations that are not real but also not impossible) delusional thoughts for one month or more that cannot be explained by any other condition. An individual's cultural beliefs merit consideration before coming to the diagnosis. Cultural beliefs also impact the content of delusions. In patients with delusional disorder, delusions(s) do not impact the functionality and the patient's behavior is not overtly bizarre

The first step in evaluation is obtaining a complete medical history while focusing on the diagnostic criteria for schizoaffective disorder.

The specific DSM-5 criteria for schizoaffective disorder are as follows:

An uninterrupted duration of illness during which there is a major mood episode (manic or depressive) in addition to criterion A for schizophrenia; the major depressive episode must include depressed mood.[1]
Criterion A for schizophrenia is as follows. Two or more of the following presentations, each present for a significant amount of time during a 1-month period (or less if successfully treated). At least 1 of these must be from the first 3 below:
Delusions
Hallucinations
Disorganized speech (eg, frequent derailment or incoherence)
Grossly disorganized or catatonic behavior
Negative symptoms (ie, diminished emotional expression or abolition) [13]
Hallucinations and delusions for 2 or more weeks in the absence of a major mood episode (manic or depressive) during the entire lifetime duration of the illness.
Symptoms that meet the criteria for a major mood episode are present for most of the total duration of both the active and residual portions of the illness.
The disturbance is not the result of the effects of a substance (eg, a drug of misuse or a medication) or another underlying medical condition.
The following are specifiers based on the primary mood episode as part of the presentation:

Bipolar type: includes episodes of mania and sometimes major depression.
Depressive type: includes only major depressive episodes.
Please note that the patient must meet the criteria for A-D above to be diagnosed with schizoaffective disorder. It is not enough to have symptoms of schizophrenia while meeting the criteria for a major mood episode. Please see the differential diagnoses and pearls sections below for more information. The next step of evaluation is the objective and physical portion. A thorough mental status examination, physical examination, and neurologic examination should be completed to help rule out other differential diagnoses.

Bipolar disorder can cause symptoms such as psychosis, including hallucinations, delusions, or jumbled thoughts. These symptoms may occur during manic or depressive episodes