The following can indicate a delusion:
- The patient expresses an idea or belief with unusual persistence or force.
- That idea appears to have an undue influence on the patient's life, and the way of life is often altered to an inexplicable extent.
- Despite his/her profound conviction, there is often a quality of secretiveness or suspicion when the patient is questioned about it.
- The individual tends to be humorless and oversensitive, especially about the belief.
- There is a quality of centrality: no matter how unlikely it is that these strange things are happening to him, the patient accepts them relatively unquestioningly.
- An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility.
- The belief is, at the least, unlikely, and out of keeping with the patient's social, cultural and religious background.
- The patient is emotionally over-invested in the idea and it overwhelms other elements of their psyche.
- The delusion, if acted out, often leads to behaviors which are abnormal and/or out of character, although perhaps understandable in the light of the delusional beliefs.
- Individuals who know the patient observe that the belief and behavior are uncharacteristic and alien.
Additional features of delusional disorder include the following:
- It is a primary disorder.
- It is a stable disorder characterized by the presence of delusions to which the patient clings with extraordinary tenacity.
- The illness is chronic and frequently lifelong.
- The delusions are logically constructed and internally consistent.
- The delusions do not interfere with general logical reasoning (although within the delusional system the logic is perverted) and there is usually no general disturbance of behavior. If disturbed behavior does occur, it is directly related to the delusional beliefs.
- The individual experiences a heightened sense of self-reference. Events which, to others, are nonsignificant are of enormous significance to him or her, and the atmosphere surrounding the delusions is highly charged.