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Delusions and Hallucinations

This PatientPlus article is written for healthcare professionals so the language may be more technical than the condition leaflets. You may find the abbreviations list helpful.

Population-based questionnaires suggest that delusions and hallucinations are far more prevalent than was originally considered.1 They do not always imply that the patient has a mental illness. However, their presence has been noted to be higher in patients with a family history of mental disorders.2 Furthermore, delusions and hallucinations should always be reviewed in the context of the patient's ethnicity and social circumstances, although interpreting such symptoms in the context of ethnocultural diversity may be challenging.3 One study propounded that delusions may be caused by problems with the functioning of the orbitofrontal part of the brain, leading to difficulty in adapting to changing circumstances and external pressures.4

Delusions

A delusion is a false belief which is firmly sustained and based on incorrect inference about reality. This belief is held despite evidence to the contrary and is not accounted for by the person's culture or religion.

Karl Jaspers, a noted psychiatrist and philosopher, described the three main criteria required for a delusion:5

  • Certainty - the patient believes the delusion absolutely.
  • Incorrigibility - the belief can not be shaken.
  • Impossibility - the delusion is without doubt untrue.

However, delusions can vary in strength over time.

Epidemiology

A UK study found that 39% of a sample of 1,000 randomly selected people completing a questionnaire (the Cardiff Beliefs Questionnaire) reported having at least one strong delusional-like belief.6 An American study of the general population reported that low self-esteem was associated with a proneness to develop delusions.7

Types of delusions

  • Monothematic - delusions are only relating to one particular topic.
  • Polythematic - range of delusional topics (seen in schizophrenia).

They can also be classified as:8

  • Primary - occur in the mind, fully formed with no preceding reasons; strongly suggestive of schizophrenia.
  • Secondary - e.g. depressed person feeling worthless.

Examples

  • Delusional jealousy (Othello's syndrome) - e.g. believing a partner is being unfaithful.
  • Capgras' delusion - belief that a close relative has been replaced by someone else who looks the same.
  • Unilateral neglect - belief that one limb or side does not exist.
  • Thought insertion - belief that someone is putting thoughts into the brain.
  • Grandiose delusion - belief of exaggerated self-worth.

One American study found that the most common delusion was persecutory, followed by religious, somatic and grandiose.9

Causes

Hallucinations

A hallucination can be described as a sensory perception which is experienced despite there being no external stimulus. Hallucinations can occur with any sense and thus be visual, auditory, olfactory, gustatory or tactile.

In pseudohallucinations the patient is aware of a stimulus which they realise is in their mind, e.g. hearing a voice. This differentiates them from hallucinations, which can be localised in a three-dimensional space outside the body.10 They are harmless, like hypnopompic and hypnagogic hallucinations.

One study found that 27% of delirious patients had visual hallucinations.11 Auditory hallucinations in adolescence are usually transient but their persistence often suggests that the psychosis will deteriorate over time.12

Epidemiology

It is estimated that many people experience hallucinations unrelated to mental illness - nearly 4% in one survey, with olfactory and gustatory types being the most common.13 Auditory hallucinations are a common feature of adolescent psychosis.12

Examples

  • Hypnagogic - occur on falling asleep and are harmless.
  • Hypnopompic - occur on waking up and are harmless.
  • Auditory - of one or more talking voices; seen commonly in schizophrenia.
  • Charles Bonnet's syndrome - visual hallucinations that blind persons experience.14

Causes15

Document references

  1. Ian K, Jenner JA, Cannon M; Psychotic symptoms in the general population - an evolutionary perspective. Br J Psychiatry. 2010 Sep;197(3):167-9. [abstract]
  2. Varghese D, Scott J, McGrath J; Correlates of delusion-like experiences in a non-psychotic community sample. Aust N Z J Psychiatry. 2008 Jun;42(6):505-8. [abstract]
  3. Vega WA, Lewis-Fernandez R; Ethnicity and variability of psychotic symptoms. Curr Psychiatry Rep. 2008 Jun;10(3):223-8. [abstract]
  4. Laws KR, Kondel TK, Clarke R, et al; Delusion-prone individuals: Stuck in their ways? Psychiatry Res. 2011 Apr 30;186(2-3):219-24. Epub 2010 Oct 28. [abstract]
  5. Spitzer M; On defining delusions. Compr Psychiatry. 1990 Sep-Oct;31(5):377-97. [abstract]
  6. Pechey R, Halligan P; The prevalence of delusion-like beliefs relative to sociocultural beliefs in the Psychopathology. 2011;44(2):106-15. Epub 2010 Dec 24. [abstract]
  7. Warman DM, Lysaker PH, Luedtke B, et al; Self-esteem and delusion proneness. J Nerv Ment Dis. 2010 Jun;198(6):455-7. [abstract]
  8. Jones H; Defining delusion. Br J Psychiatry. 2004 Oct;185:354-5.
  9. Cannon BJ, Kramer LM; Delusion content across the 20th century in an American psychiatric hospital. Int J Soc Psychiatry. 2011 Mar 18. [abstract]
  10. El-Mallakh RS, Walker KL; Hallucinations, psuedohallucinations, and parahallucinations. Psychiatry. 2010 Spring;73(1):34-42. [abstract]
  11. Webster R, Holroyd S; Prevalence of psychotic symptoms in delirium. Psychosomatics. 2000 Nov-Dec;41(6):519-22. [abstract]
  12. De Loore E, Gunther N, Drukker M, et al; Persistence and outcome of auditory hallucinations in adolescence: a longitudinal Schizophr Res. 2011 Apr;127(1-3):252-6. Epub 2011 Feb 18. [abstract]
  13. Johns LC, Nazroo JY, Bebbington P, et al; Occurrence of hallucinatory experiences in a community sample and ethnic variations. Br J Psychiatry. 2002 Feb;180:174-8. [abstract]
  14. Kester EM; Charles Bonnet syndrome: case presentation and literature review. Optometry. 2009 Jul;80(7):360-6. [abstract]
  15. Cummings JL, Miller BL; Visual hallucinations. Clinical occurrence and use in differential diagnosis. West J Med. 1987 Jan;146(1):46-51.
  16. Ergun U, Bozbas A, Akin U, et al; Musical hallucinations and Parkinson disease. Neurologist. 2009 May;15(3):150-2. [abstract]
  17. Elliott B, Joyce E, Shorvon S; Delusions, illusions and hallucinations in epilepsy: 1. Elementary phenomena. Epilepsy Res. 2009 Aug;85(2-3):162-71. Epub 2009 May 6. [abstract]
  18. Shevlin M, Murphy J, Read J, et al; Childhood adversity and hallucinations: a community-based study using the Soc Psychiatry Psychiatr Epidemiol. 2010 Oct 8. [abstract]

Internet and further reading

  • Knight WD, Fox NC, Rossor MN, et al; The cultural context of visual hallucinations. Postgrad Med J. 2008 Feb;84(988):103-5. [abstract]
  • Schlimme JE; Paranoid atmospheres: psychiatric knowledge and delusional realities. Philos Ethics Humanit Med. 2009 Sep 17;4:14. [abstract]
  • Teeple RC, Caplan JP, Stern TA; Visual hallucinations: differential diagnosis and treatment. Prim Care Companion J Clin Psychiatry. 2009;11(1):26-32.
  • Thornhill, C; Karl Jaspers,The Stanford Encyclopedia of Philosophy (Spring 2011 Edition), Edward N. Zalta (ed.)

Acknowledgements

EMIS is grateful to Dr Laurence Knott for writing this article and to Dr Gurvinder Rull for earlier versions. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2011.
Document ID: 1715
Document Version: 22
Document Reference: bgp586
Last Updated: 26 Apr 2011
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