Delusional Disorder

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Delusional Disorder



Causes and symptoms








Delusional disorder is characterized by the presence of recurrent, persistent non-bizarre delusions.

Delusions are irrational beliefs, held with a high level of conviction, that are highly resistant to change even when the delusional person is exposed to forms of proof that contradict the belief. Non-bizarre delusions are considered to be plausible; that is, there is a possibility that what the person believes to be true could actually occur a small proportion of the time. Conversely, bizarre delusions focus on matters that would be impossible in reality. For example, a non-bizarre delusion might be the belief that one’s activities are constantly under observation by federal law enforcement or intelligence agencies, which actually does occur for a small number of people. By contrast, a man who believes he is pregnant with German Shepherd puppies holds a belief that could never come to pass in reality. Also, for beliefs to be considered delusional, the content or themes of the beliefs must be uncommon in the person’s culture or religion. Generally, in delusional disorder, these mistaken beliefs are organized into a consistent world-view that is logical other than being based on an improbable foundation.

In addition to giving evidence of a cluster of interrelated non-bizarre delusions, persons with delusional disorder experience hallucinations far less frequently than do individuals with schizophrenia or schizoaffective disorder.


Unlike most other psychotic disorders, the person with delusional disorder typically does not appear obviously odd, strange or peculiar during periods of active illness. Yet the person might make unusual choices in day-to-day life because of the delusional beliefs. Expanding on the previous example, people who believe they are under government observation might seem typical in most ways but could refuse to have a telephone or use credit cards in order to make it harder for “those Federal agents” to monitor purchases and conversations. Most mental health professionals would concur that until the person with delusional disorder discusses the areas of life affected by the delusions, they would experience difficulty in distinguishing the patient from members of the general public who are not psychiatrically disturbed. Another distinction of delusional disorder compared with other psychotic disorders is that hallucinations are either absent or occur infrequently.

The person with delusional disorder may or may not come to the attention of mental health providers. Typically, while people with delusional disorder may be distressed about the delusional “reality,” they may not have the insight to see that anything is wrong with the way they are thinking or functioning. Regarding the earlier example, those experiencing delusion might state that the only thing wrong or upsetting in their lives is that the government is spying, and if the surveillance would cease, so would the problems. Similarly, people with the disorder attribute any obstacles or problems in functioning to the delusional reality, separating it from their internal control. Furthermore, whether unable to get a good job or maintain a romantic relationship, the difficulties would be blamed on “government interference” rather than on their own failures or omissions. Unless the form of the delusions causes illegal behavior, somehow affects an ability to work, or otherwise deal with daily activities, the person with delusional disorder may adapt well enough to navigate life without coming to clinical attention. When people with delusional disorder decide to seek mental health care, the motivation for getting treatment is usually to decrease the negative emotions of depression, fearfulness, rage, or constant worry caused by living under the cloud of delusional beliefs, not to change the unusual thoughts themselves.

Forms of delusional disorder

An important aspect of delusional disorder is the identification of which form of delusion characterizes the individual. The most common form of delusional disorder is the persecutory or paranoid subtype, in which the patients are certain that others are striving to harm them.

In the erotomanic form of delusional disorder, the primary delusional belief is that some important person is secretly in love with the individual. The erotomanic type is more common in women than men. Erotomanic delusions may prompt stalking the love object and even violence against the beloved or those viewed as potential romantic rivals.

The grandiose subtype of delusional disorder involves the conviction of one’s importance and uniqueness, and takes a variety of forms: believing that one has a distinguished role, has some remarkable connections with important persons, or enjoys some extraordinary powers or abilities.

In the somatic subtype, there is excessive concern and irrational ideas about bodily functioning, which may include worries regarding infestation with parasites or insects, imagined physical deformity, or a conviction that one is emitting a foul stench when there is no problematic odor.

The form of disorder most associated with violent behavior, usually between romantic partners, is the jealous subtype of delusional disorder. Patients are firmly convinced of the infidelity of a spouse or partner, despite contrary evidence and based on minimal data (like a messy bedspread or more cigarettes than usual in an ashtray, for instance). People with delusional jealousy may gather scraps of conjectured “evidence,” and may try to constrict their partners’ activities or confine them to home. Delusional disorder cases involving aggression and injury toward others have been most associated with this subtype.

Delusion and other disorders

Even though the main characteristic of delusional disorder is a noticeable system of delusional beliefs, delusions may occur in the course of a large number of other psychiatric disorders. Delusions are often observed in persons with other psychotic disorders such as schizophrenia and schizoaffective disorder. In addition to occurring in the psychotic disorders, delusions also may be evident as part of a response to physical, medical conditions (such as brain injury or brain tumors), or reactions to ingestion of a drug.

Delusions also occur in the dementias, which are syndromes wherein psychiatric symptoms and memory loss result from deterioration of brain tissue. Because delusions can be shown as part of many illnesses, the diagnosis of delusional disorder is partially conducted by process of elimination. If the delusions are not accompanied by persistent, recurring hallucinations, then schizophrenia and schizoaffective disorder are not appropriate diagnoses. If the delusions are not accompanied by memory loss, then dementia is ruled out. If there is no physical illness or injury or other active biological cause (such as drug ingestion or drug withdrawal), then the delusions cannot be attributed to a general medical problem or drug-related causes. If delusions are the most obvious and pervasive symptom, without hallucinations, medical causation, drug influences or memory loss, then delusional disorder is the most appropriate categorization.

Because delusions occur in many different disorders, some clinician-researchers have argued that there is little usefulness in focusing on what diagnosis the person has been given. Those who ascribe to this view believe it is more important to focus on the symptom of delusional thinking, and find ways to have an effect on delusions, whether they occur in delusional disorder or schizophrenia or schizoaffective disorder. The majority of psychotherapy techniques used in delusional disorder come from symptom-focused (as opposed to diagnosis-focused) researcher-practitioners.

Causes and symptoms


Because clear identification of delusional disorder has traditionally been challenging, scientists have conducted far less research relating to the disorder than studies for schizophrenia or mood disorders. Still, some theories of causation have developed, which fall into several categories.


Close relatives of persons with delusional disorder have increased rates of delusional disorder and paranoid personality traits. They do not have higher rates of schizophrenia, schizoaffective disorder or mood disorder compared to relatives of non-delusional persons. Increased incidence of these psychiatric disorders in individuals closely genetically related to persons with delusional disorder suggest that there is a genetic component to the disorder. Furthermore, a number of studies comparing activity of different regions of the brain in delusional and non-delusional research participants yielded data about differences in the functioning of the brains between members of the two groups. These differences in brain activity suggest that, persons neurologically with delusions tend to react as if threatening conditions are consistently present. Non-delusional persons only show such patterns under certain kinds of conditions where the interpretation of being threatened is more accurate. With both brain activity evidence and family heritability evidence, a strong chance exists that there is a biological aspect to delusional disorder.


An elaborate term for thinking is “cognitive processing.” Delusions may arise from distorted ways people have of explaining life to themselves. The most prominent cognitive problems involve the manner in which people with delusion develop conclusions both about other people, and about causation of unusual perceptions or negative events. Studies examining how people with delusions develop theories about reality show that the subjects have ideas which they tend to reach an inference based on less information than most people use. This “jumping to conclusions” bias can lead to delusional interpretations of ordinary events. For example, developing flu-like symptoms coinciding with the week new neighbors move in might lead to the conclusion, “the new neighbors are poisoning me.” The conclusion is drawn without considering alternative explanations—catching an illness from a relative with the flu, that a virus seems to be going around at work, or that the tuna salad from lunch at the deli may have been spoiled. Additional research shows that persons prone to delusions “read” people differently than non-delusional individuals do. Whether they do so more accurately or particularly poorly is a matter of controversy. Delusional persons develop interpretations about how others view them that are distorted. They tend to view life as a continuing series of threatening events. When these two aspects of thought co-occur, a tendency to develop delusions about others wishing to do them harm is likely.


Some predisposed persons might experience the onset of an ongoing delusional disorder when coping with life and maintaining high self-esteem becomes a significant challenge. In order to preserve a positive view of oneself, a person views others as the cause of personal difficulties that may occur. This can then become an ingrained pattern of thought.


The criteria that define delusional disorder are furnished in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Text Revision, or DSM-IV-TR, published by the American Psychiatric Association. The criteria for delusional disorder are as follows:

  • non-bizarre delusions that have been present for at least one month
  • absence of obviously odd or bizarre behavior
  • absence of hallucinations, or hallucinations that only occur infrequently in comparison to other psychotic disorders
  • no memory loss, medical illness or drug or alcohol-related effects are associated with the development of delusions


The base rate of delusional disorder in adults is unclear. The prevalence is estimated at 0.025-0.03%, lower than the rates for schizophrenia (1%). Delusional disorder may account for 1-2% of admissions to inpatient psychiatric hospitals. Age at onset ranges from 18-90 years, with a mean age of 40 years. More females than males (overall) develop delusional disorder, especially the late onset form that is observed in the elderly.


Client interviews focused on obtaining information about the individual’s life situation and past history aid in identification of delusional disorder. With the client’s permission, the clinician obtains details from earlier medical records, and engages in thorough discussion with the client’s immediate family—helpful measures in determining whether delusions are present. The clinician may use a semi-structured interview called a mental status examination to assess the patient’s concentration, memory, understanding the individual’s situation and logical thinking. The mental status examination is intended to reveal peculiar thought processes in the patient. The Peters Delusion Inventory (PDI) is a psychological test that focuses on identifying and understanding delusional thinking; but its use is more common in research than in clinical practice.

Even using the DSM-IV-TR criteria, classification of delusional disorder is relatively subjective. The criteria “non-bizarre” and “resistant to change” and “not culturally accepted” are all subject to very individual interpretations. They create variability in how professionals diagnose the illness. The utility of diagnosing the syndrome rather than focusing on successful treatment of delusion in any form of illness is debated in the medical community. Some researchers further contend that delusional disorder, currently classified as a psychotic disorder, is actually a variation of depression and might respond better to antidepressants or therapy more similar to that utilized for depression. Also, the meaning and implications of “culturally accepted” can create problems. The cultural relativity of “delusions”—most evident where the beliefs shown are typical of the person’s subculture or religion yet would be viewed as strange or delusional by the dominant culture—can force complex choices to be made in diagnosis and treatment. An example could be that of a Haitian immigrant to the United States who believed in voodoo. If that person became aggressive toward neighbors issuing curses or hexes, believing that death is imminent at the hands of those neighbors, a question arises. The belief is typical of the individual’s subculture, so the issue is whether it should be diagnosed or treated. If it were to be treated, whether the remedy should come through Western medicine, or be conducted through voodoo shamanistic treatment is the problem to be solved.


Delusional disorder treatment often involves atypical (also called novel or newer-generation) antipsychotic medications, which can be effective in some patients. Risperidone (Risperdal), quetiapine (Seroquel), and olanzapine (Zyprexa) are all examples of atypical or novel antipsychotic medications. If agitation occurs, a number of different antipsychotics can be used to conclude the outbreak of acute agitation. Agitation, a state of frantic activity experienced concurrently with anger or exaggerated fearfulness, increases the risk that the client will endanger self or others. To decrease anxiety and slow behavior in emergency situations where agitation is a factor, an injection of haloperidol (Haldol) is often given usually in combination with other medications (often lorazepam, also known as Ativan). Agitation in delusional disorder is a typical response to severe or harsh confrontation when dealing with the existence of the delusions. It can also be a result of blocking the individual from performing inappropriate actions the client views as urgent in light of the delusional reality. A novel antipsychotic is generally given orally on a daily basis for ongoing treatment meant for long term effect on the symptoms. Response to antipsychotics in delusional disorder seems to follow the “rule of thirds,” in which about one-third of patients respond somewhat positively, one-third show little change, and one-third worsen or are unable to comply.

Cognitive therapy has shown promise as an emerging treatment for delusions. The cognitive therapist tries to capitalize on any doubt the individual has about the delusions; then attempts to develop a joint effort with the patient to generate alternative explanations, assisting the client in checking the evidence. This examination proceeds in favor of the various explanations. Much of the work is done by use of empathy, asking hypothetical questions in a form of therapeutic Socratic dialogue—a process that follows a basic question and answer format, figuring out what is known and unknown before reaching a logical conclusion. Combining pharmacotherapy with cognitive therapy integrates both treating the possible underlying biological problems and decreasing the symptoms with psychotherapy.


Hallucinations —False sensory perceptions. A person experiencing a hallucination may “hear” sounds or “see” people or objects that are not really present. Hallucinations can also affect the senses of smell, touch, and taste.

Psychosis or psychotic symptoms —Disruptions in perceiving reality, thinking logically, and speaking or behaving in normal fashion. Hallucinations, delusions, catatonic behavior and peculiar speech are all symptoms of psychosis. In DSM-IV-TR, psychosis is usually one feature of an over-arching disorder, not a disorder in itself (with the exception of the diagnosis psychosis not otherwise specified.


Evidence collected to date indicates about 10% of cases will show some improvement of delusional symptoms though irrational beliefs may remain; 33-50% may show complete remission; and, in 30-40% of cases there will be persistent non-improving symptoms. The prognosis for clients with delusional disorder is largely related to the level of conviction regarding the delusions and the openness the person has for allowing information that contradicts the delusion.


Little work has been done thus far regarding prevention of the disorder. Effective means of prevention have not been identified.

See alsoDementia; Depression (with psychotic features); Paranoia; Paranoid personality disorder; Schizoaffective disorder; Schizophrenia.



American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revised. Washington, DC: American Psychiatric Association, 2000.

Chadwick, Paul, Max Birchwood, and Peter Trower. Cognitive Therapy for Delusions, Voices and Paranoia. Chichester, United Kingdom: Wiley and Sons, 1996.

Fuller, Matthew, and M. Sajatovic. Drug Information for Mental Health Hudson, Ohio: Lexi-comp, 2000.


Bentall, Richard P., Rhiannon Corcoran, Robert Howard, Nigel Blackwood, and Peter Kinderman. “Persecutory delusions: A review and theoretical integration.” Clinical Psychology Review 21, no. 8 (2001): 1143–1193.

Garety, Philippa A. and Daniel Freeman. “Cognitive approaches to delusions: A critical review of theories and evidence.” British Journal of Clinical Psychology 38 (1999): 113–154.

Haddock, Gillian, Nicholas Tarrier, William Spaulding, Lawrence Yusupoff, Caroline Kinney and Eilis McCarthy. “Individual cognitive therapy in the treatment of hallucinations and delusions: A review.” Clinical Psychology Review 18, no. 7 (1998): 821–838.


National Alliance for the Mentally Ill. Colonial Place Three, 2107 Wilson Blvd., Suite 300, Arlington, VA 22201. Telephone: (703) 524-7600. NAMI HelpLine: 1-800-950-NAMI (6264). <>.

Deborah Rosch Eifert, Ph.D.