History of the first identification of delusional disorder is hampered by its relative rareness, the variety of theories regarding its etiology, and changing definitions in recent history. Freud believed that delusions were part of a healing process. In 1896, he described projection as the main defense mechanism in paranoia (now referred to as delusional disorder). He also theorized that individuals with paranoia (delusional disorder) utilized the defense mechanisms of denial and projection to defend against unconscious homosexual tendencies. Although careful studies of clients with delusions have been unable to corroborate Freud’s theories regarding the dynamics of homosexual tendencies, his major contribution was to demonstrate the role of projection in the formation of delusional disorders (Sadock & Sadock, 2003).

Shared psychotic disorder, also referred to as shared paranoid disorder, induced psychotic disorder, and double insanity, was first described in 1651 in a case of phantom pregnancy associated with two sisters. In 1877, the term folie à deux (which refers to two individuals who have a close relationship and shared delusions) was used in a classic report by Lasegue and Falret. Almost a century later (1942), a classification of four subtypes of folie à deux was published by Gralnick: folie imposèe (delusions of a person with psychosis are transferred to a person who is mentally sound); folie simultanèe (simultaneous appearance of an identical psychosis occurs in two individuals who are intimately associated and morbidly predisposed); folie communiquèe (the recipient develops psychosis after a long period of resistance and maintains the symptoms even after separation); and folie induite (new delusions are adopted by an individual with psychosis who is under the influence of another individual with psychosis). A literature review by Sharon, Sharon, Eliyahu, and Shteynman (2006) revealed the existence of several complex cases of shared psychotic disorders (husband/wife, mother/daughter, twins). Their article sheds light on the seriousness of the disorder, complications associated with the disorder, and the need for treatment.

Although the cause of delusional disorders is unknown, several predisposing factors have been identified. These include risk factors such as:

Research has demonstrated that delusions can also result from an identifiable neurologic disease, primarily those diseases that affect the limbic system and the basal ganglia. Clients with a neurologic condition may have intact cerebral cortical functioning, but exhibit complex delusions that are referred to as content-specific delusions (CSDs) to distinguish them from the delusions exhibited in psychiatric disorders such as paranoid schizophrenia. Content-specific delusions are also associated with focal lesions of the frontal lobe or right hemisphere of the brain (Sadock & Sadock, 2003).

Information about the familial pattern of delusional disorders is conflicting. Some studies have found that delusional disorders are more common among relatives of individuals with schizophrenia than would be expected by chance. Other studies have found no familial relationship between delusional disorders and schizophrenia (American Psychiatric Association [APA], 2000).

Although often difficult to differentiate from paranoid schizophrenia, the delusions in delusional disorder are characteristically systematized (an ordered grouping of sustained false beliefs) and nonbizarre. Nonbizarre delusions involve situations that could occur in real life, usually involving phenomena that, although not real, are possible (Sadock & Sadock, 2003).

Although nonbizarre delusions can occur at a younger age, the typical age of onset is usually middle or late adult life. Clients with nonbizarre delusions usually verbalize extreme suspiciousness, jealousy, and distrust, and are generally convinced that others intend to do them harm. They may complain about various injustices, and frequently instigate legal actions as they verbalize resentment, anger, and grandiose ideas. Social and marital functioning are often impaired, although the client preserves daily, intellectual, and occupational functioning.

Other clinical symptoms may include social isolation, seclusiveness, or eccentric behavior. Anxiety or depression may occur as the client attempts to cope with delusional thoughts. Clients rarely seek treatment. Usually clients are brought to the attention of mental health professionals by friends, relatives, or associates who are concerned about their behavior.

Clients with delusional disorders also may experience CSDs, occurring at any time. CSDs are not categorized in the DSM-IV-TR. Clients with CSDs are usually described as forthcoming and cooperative. They insist that their delusions are true, but also admit to puzzlement or bemusement regarding aspects of the delusion. They are more likely to confabulate explanations for their delusions rather than become defensive and hostile (Malloy & Salloway, 1999). Types of CSDs include delusions of place, delusions of person, sexual delusions, and somatic delusions.

According to DSM-IV-TR criteria, delusional disorder is differentiated from schizophrenia in that clients with delusional disorder do not have prominent or sustained hallucinations associated with schizophrenia. However, clients may verbalize the presence of tactile, olfactory, or auditory hallucinations consistent with their delusions. Delusions, as noted earlier, are not bizarre, but rather could conceivably occur in real life (eg, client believes he or she is being poisoned or that someone has tampered with the brakes in his or her car). The delusions are not due to any other mental disorder such as schizophrenia, and are not the direct physiologic effects of a substance or the direct result of a general medical condition.

Clients with delusional disorder have no insight into their condition. They refuse to acknowledge negative feelings, thoughts, motives, or behaviors in themselves and project such feelings onto others by blaming others for their problems. They also spend much time confirming suspicions and defending themselves against imagined persecution. Such self-centered thoughts, in which everything is taken personally, are called ideas of reference.

The DSM-IV-TR identifies five subtypes of delusional disorder: persecutory, conjugal or jealous, erotomanic, grandiose, and somatic. In all subtypes, mood changes, including irritability, anger, depression, and violence, may occur. Legal difficulties also may arise. Clients may be subjected to unnecessary medical tests and procedures. Social, marital, or work problems are common. However, cognitive disorganization or emotional deterioration usually does not occur. The type of delusional disorder with which a client is diagnosed is based on the predominant delusional theme, because cases with more than one theme are frequent. See Clinical Example 28-1.

As noted earlier in this chapter, shared psychotic disorder, or folie à deux, involves two individuals who have a close relationship and share the same delusion. This occurrence is attributed to the strong influence of the more dominant (primary case or inducer) person over the submissive (secondary case) individual. Traditional views believed this disorder was seen more frequently in women who were isolated by language, culture, or geography; however, literature analysis revealed that females and males are affected equally. Such persons are often related by blood or marriage and have lived together for an extended period of time. The incidence in married or common-law couples is equal to that in siblings. Contributing factors include low intelligence, sensory impairment, cerebrovascular disease, and alcohol abuse. Age used to be
considered a contributing factor (ie, submissive individual was younger than the dominant person); however, recent views have shown that the submissive individual has an equal chance of being either younger or older than the dominant individual. This disorder has been diagnosed in twins and in individuals, both of whom had a chronic psychotic disorder. This disorder also has occurred in a group of individuals or in families in which the parent is the primary case (inducer) (Sadock & Sadock, 2003

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