Visual hallucinations

Visual hallucinations are relatively uncommon, and can be due to a variety of 'organic' brain diseases, affecting a variety of regions of the brain.  The use of the term organic here is by convention, and should not be taken to imply absence of brain dysfunction in psychiatric illness.

Clinical presentation

Visual hallucinations can take various forms and should be distinguished from visual distortions or pseudohallucinations. They can be divided into simple and complex forms:

• simple hallucinations
  • typically due to irritation or stimulation of the primary visual cortex (e.g. tumors, epilepsy) 
  • brief, uniform and stereotyped
  • flashes of light and color or indistinct forms
• complex visual hallucinations
  • disruption to the wider visual system
  • complex visual percepts
    • branching or tessellated patterns
    • people and/or animals
    • complex scenes often associated with sensory distortions

Of interest, the patient's insight and response to these hallucinations is variable. In some cases, such as Lilliputian hallucinations (miniature people in lines or groups often performing strange actions), the hallucinations are not distressing, but rather elicit curiosity or wonder.  In other settings, for example those due to psychiatric disturbance, delirium or intoxication/withdrawal are often frightening.

Pathology

Etiology

A number of conditions are known to be associated with visual hallucinations including:

• delirium including secondary to drugs such as cocaine, methamphetamine
• psychoses (schizophrenia, schizoaffective disorder)
• occipital lesions (e.g. tumors, vascular malformations, strokes, epileptogenic foci)
  • Anton syndrome: may be seen after occipital infarcts
• migraine, posterior reversible encephalopathy syndrome (PRES)
• dementia
  • Lewy body dementia: >20% experience visual hallucinations
  • Parkinson disease dementia: 50% experience visual hallucinations
  • Alzheimer disease
  • posterior cortical atrophy
  • Creutzfeldt-Jakob disease (CJD): particularly the Heidenhain variant
• peduncular hallucinosis: due to infarcts of the midbrain
• thalamic lesions (e.g. top of the basilar syndrome)
• Charles Bonnet syndrome
• sleep-related, especially in narcolepsy
  • hypnagogic hallucinations
  • hypnopompic hallucinations
• exogenous agents
  • hallucinogens: mescaline, psilocybin, lysergic acid diethylamide (LSD), phencyclidine (PCP), ecstasy (MDMA), atropine, dopamine agonists
  • alcohol withdrawal i.e. delirium tremens
• genetic metabolic disorders
  • homocysteine remethylation defects
  • urea cycle defects
  • GM2 gangliosidosis
  • Niemann-Pick disease type C
  • α-mannosidosis