Delusions are fixed beliefs that do not change, even when a person is presented with conflicting evidence. Delusions are considered "bizarre" if they are clearly implausible and peers within the same culture cannot understand them. An example of a bizarre delusion is when an individual believes that his or her organs have been replaced with someone else's without leaving any wounds or scars. An example of a nonbizarre delusion is the belief that one is under police surveillance, despite a lack of evidence.
Delusional disorder refers to a condition in which an individual displays one or more delusions for one month or longer. Delusional disorder is distinct from schizophrenia and cannot be diagnosed if a person meets the criteria for schizophrenia. If a person has delusional disorder, functioning is generally not impaired and behavior is not obviously odd, with the exception of the delusion. Delusions may seem believable at face value, and patients may appear normal as long as an outsider does not touch upon their delusional themes. Also, these delusions are not due to a medical condition or substance abuse.
There are several different types of delusional disorders, and each type captures a particular theme within a person's delusions.
- Erotomanic: An individual believes that a person, usually of higher social standing, is in love with him or her.
- Grandiose: An individual believes that he or she has some great but unrecognized talent or insight, a special identity, knowledge, power, self-worth, or relationship with someone famous or with God.
- Jealous: An individual believes that his or her partner has been unfaithful.
- Persecutory: An individual believes that he or she is being cheated, spied on, drugged, followed, slandered, or somehow mistreated.
- Somatic: An individual believes that he or she is experiencing physical sensations or bodily dysfunctions, such as foul odors or insects crawling on or under the skin, or is suffering from a general medical condition or defect.
- Mixed: An individual exhibits delusions that are characterized by more than one of the above types, but no one theme dominates.
- Unspecified: An individual's delusions do not fall into the described categories or cannot be clearly determined.
The most frequent type of delusional disorder is persecutory. Even so, this condition is rare, with an estimated 0.2 percent of people experiencing it at some point in their lifetime. Delusional disorder is equally likely to occur in males and females. Onset can vary from adolescence to late adulthood but tends to appear later in life.