Charles Bonnet Syndrome: Definition and Management
Charles Bonnet syndrome (CBS) is characterized by recurrent, vivid visual hallucinations in patients with vision impairment who maintain insight that their perceptions are not real, without other neurological or medical diagnoses explaining the hallucinations. 1
Diagnostic Criteria
CBS is defined by four key features:
- Recurrent, vivid visual hallucinations 1
- Patient insight that what is seen is not real 1, 2
- No other neurological or medical diagnosis explaining the hallucinations 1
- Some degree of vision loss 1
Epidemiology and Prevalence
- Affects patients with any level of vision impairment 1
- Prevalence ranges from 15% to 60% among patients with ophthalmologic disorders, depending on definition and population studied 1
- More than 20% of people with vision loss experience these hallucinations 1
- Occurs in approximately 13% of patients with Age-Related Macular Degeneration (AMD) 3
- Higher incidence in patients with massive loss of peripheral visual field 3
Pathophysiology
- Attributed to a cortical-release phenomenon resulting from lack of afferent visual information 1
- Represents a form of "phantom vision" due to deafferentiation of visual association areas in the cerebral cortex 3
- Cognitive defects, social isolation, and sensory deprivation may contribute to the etiology 3
- Sensory deprivation and low arousal levels appear to favor hallucination occurrence 2
- A possible link between CBS and cognitive dysfunction is under current research 1
Clinical Presentation
- Hallucinations are typically complex and well-defined 3, 2
- Often described as "Lilliputian hallucinations" where objects appear much smaller than normal (micropsia) 3
- Patients maintain full insight into the unreal nature of their hallucinations 2
- Can occur with various types of vision loss:
Differential Diagnosis
CBS must be distinguished from hallucinations associated with:
- Drug or alcohol abuse (delirium tremens) 3
- Alice in Wonderland syndrome 3
- Psychosis or schizophrenia 3, 4
- Dementia 3
- Narcolepsy 3
- Epilepsy 3
- Parkinson's disease 3
- Brain tumors 3
- Migraine 3
- Long-term sleep deprivation 3
Management Approach
Patient Education and Reassurance
- Educate patients and family/caregivers that phantom vision is common in visually impaired people 1
- Reassure patients that hallucinations do not indicate mental illness 2
- Discussion often leads to significant relief and decreased anxiety 1, 2
Non-Pharmacological Management
- Self-management techniques that may reduce hallucinations:
- Transcranial direct-current stimulation (tDCS) has shown promise in reducing hallucination frequency in a small trial 1
Pharmacological Management
- Limited evidence for efficacy of pharmacological treatments 1
- Medications are generally based on anecdotal data rather than robust clinical evidence 4
Psychological Support
- Consider psychological therapies and support groups for patients with vision loss 1
- Psychological support may help reduce the impact of hallucinations 1
Red Flags and Warning Signs
Atypical features that should raise suspicion of diagnoses other than CBS include:
- Lack of insight into the unreal nature of images despite explanation 1
- Hallucinations that interact with the patient 1
- Associated neurological signs or symptoms 1
- Evolution to include psychotic symptoms (rare but possible) 5
Clinical Pearls
- CBS is frequently underdiagnosed - in one study, only 1 of 16 patients who consulted a doctor received the correct diagnosis 2
- Although hallucinations can cause anxiety, they lack personal meaning in approximately 77% of patients 2
- Only about 28% of patients report significant distress from the hallucinations 2
- All patients benefit from reassurance that their hallucinations do not indicate mental illness 2
- CBS can occur in conjunction with other psychiatric conditions, complicating diagnosis and management 5