Odd Ideas - Delusions and Hallucinations

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 delusion¹

• 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.

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 as²

• 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 syndrome) - e.g. believe 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• Capgras delusion - belief that a close relative has been replaced by someone else who looks the same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 in to the brain
• Grandiose delusion - belief of exaggerated self worth

A hallucination can be described as a sensory perception which is experienced despite there being no external stimulus. They 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 in their mind e.g. hearing a voice.² These are also harmless like hypnopompic and hypnagogic hallucinations.

Auditory hallucinations suggest psychosis where as tactile and visual hallucinations point to organic illnesses.² Up to 75% of delirious patients will experience visual hallucinations.³

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 commonest.⁴

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 syndrome - visual hallucinations that blind persons experience