A delusion is a false belief that is not susceptible to argument and that is inconsistent with the subject’s sociocultural background. Bordering on delusion is the overvalued idea, a notion that may be eccentric rather than false but that becomes a governing force in the patient’s life.
It is not always easy to draw the line between an eccentric individual, somebody who holds unfamiliar views that are nevertheless consistent with a different sociocultural system, and a deluded person. Indeed, some people drift across the misty boundaries between these categories. An active delusion, however, is rigid, unshakable, and self-evident. It dominates the subject’s life, subordinating all other matters. It is private, idiosyncratic, ego-centered, and inconsistent with the common experience of people from the same background. A delusion, therefore, isolates the subject from others and alienates them from him or her.
Severe sensory deprivation, or exhaustion and physical privation, may lead to delusional misinterpretation, often associated with wish-fulfilling hallucinations. A delusion can act as a transcendental escape from an existential wasteland. This is the ground from which cosmic, messianic, and redemptive delusions grow.
As for the content of delusions, the commonest are of persecution, jealousy, love, grandeur, disease, poverty, and guilt. Delusions of persecution are most frequently encountered in schizophreniform disorders or schizophrenia, paranoid disorders, organic mental disorder (especially alcoholic hallucinosis, amphetamine delirium or delusional disorder, other hallucinogenic syndromes, epilepsy, and all forms of delirium) and, less commonly, in melancholia or during transitory psychotic breaks in the life-course of borderline personality. The patient may perceive others as talking conspiratorially about him or her (delusions of reference) or spying on him or her. External agencies (eg, communists, federal bureau of investigation (FBI), freemasons) are regarded as acting in concert and disconcerting the subject with radiation, poisonous gases, radio and television, intruders, assassins, and so on. The patient often alludes to the use of tape recorders, cameras, and other surveillance paraphernalia. Delusions of poisoning, particularly by the spouse, are sometimes encountered.
Delusions of jealousy occur in the same syndromes as delusions of persecution but are especially likely in association with alcoholism in men. In that case, delusions of marital infidelity (possibly related to alcoholic impotence) are characteristic, and the patient closely scrutinizes his wife and her belongings for evidence of adultery.
Delusions of grandeur occur in mania, schizophrenia, paranoid disorders, and organic delusional syndromes (eg, neurosyphilis). In mania and organic grandiosity, the patient’s megalomania (eg, of being God, the governor, the Virgin Mary, Napoleon) are in line with his or her general high spirits. In schizophrenia and paranoid disorders, an inflated sense of importance may be reinforced by auditory hallucinations and the grandiosity of a delusional explanation for ideas of persecution: Why else would important agencies (eg, the FBI, the Vatican, the PLO) be persecuting the patient?
Erotic delusions (erotomania) are more common in female schizophrenic or paranoid patients. A lonely person develops a crush on another, often a celebrity or prominent citizen. Fantasies evolve into delusions, and the subject bombards the other person with telephone calls and messages. The failure of the loved one to reciprocate is put down to conspiratorial forces that stand in the way of destiny. In schizophrenia, the patient may receive erotic hallucinations from the beloved.
Somatic delusions, usually of disease or ill health, occur in many psychiatric disorders. Schizophrenic patients may have bizarre complaints, possibly in an attempt to explain somatic hallucinatory experiences, for example, of blood running backward in the head, of radiation being trained on the genitals by an outside agency, or of objects placed inside the body by malevolent forces. In melancholia, the patient may have delusions of being dead (no blood in the body), of the internal organs rotting away, or of the brain being destroyed by syphilis, in retribution for an unpardonable sin. The boundary between hypochondriasis, disease phobia, and disease conviction on the one hand and somatic delusions on the other may be difficult to define.
Melancholic patients are prone to delusions of poverty and delusions of nihilism. The future is hopeless, the present desolate, the patient destitute and abandoned to a bleak fate. Depressive patients may also complain of inordinate guilt, the most extreme punishments being meted out to them for unremarkable, ancient transgressions.