Charles Bonnet syndrome

Historical Perspective Charles Bonnet syndrme (CBS) was first discovered by Charles Bonnet a Swiss philosopher, in 1760 when his visually impaired grandfather started having hallucinations. Later on, the term was coined by a Swiss neurologist named as Georges de Morsier, when he noticed similar conditions in other elderly individuals . CBS was found to have occurred in visually impaired patients who are otherwise mentally healthy. Patients with CBS often have complex visual hallucinations which are disturbing . These hallucinations are vivid, formed, recurrent and of realistic objects or people Classification CBS can be classified into different categories based on physical, and etiological factors and onset time. Based on other Comorbid conditions: Primary CBS: CBS is considered primary if it occurred due to visual impairment with no other neurological issue. Secondary CBS: CBS is considered secondary if it occurs along with other neurological conditions such as dementia, Parkinson's, etc. It is also classified based on the type of hallucinations: Simple CBS: When hallucination involves basic shapes, colors, and patterns. Complex CBS: When hallucination involves detailed pictures, objects,s, etc. Classification based on frequency of onset: Transient: Hallucinations that occur irregularly and spontaneously but are not persistent. Persistent: Hallucinations that occur regularly or continuously over time. Pathophysiology Hallucinations in CBS are purely visual, occur in a conscious state when a patient is awake and alert Neurophysiological changes:

A study conducted in 1998 found a correlation between hallucination and the functional anatomy of the occipital lob. Two experiments were conducted by Ffytche DH, one enrolled six patients who were asked to report the onset and offset of hallucination. The whole process of investigating the activity took 5 minutes. They were investigated through functional magnetic resonance imaging (fMRI). Hallucinations in CBS are corelated with functional activity in the ventral occipital lobe, within or around the fusiform gyrus (Brodmann area (BA) 37). It was observed that patients with different hallucination patterns had different areas involved, with colored hallucination having increased activity in the fusiform gyrus, area V4, patients with black and white hallucination had activity outside this region, and hallucinated objects involved activity in the middle fusiform gyrus. Another experiment enrolled 2 groups, one with visual impairment and another consisting of controls who never had visual hallucinations. Both were gone through scanning of brain regions when exposed to non-specific visual stimuli, and abnormal patterns of activities were observed. Visual stimulus evoked activity in different areas but failed to do so in fusiform and lingual gyri of CBS group Neurochemical Imbalance: One of a study conducted in USA observed Involvement of neurotransmitters such as acetylcholine and dopamine in causing hallucination Causes Primarily Charles bonnet syndrome is caused by severe visual impairment. Investigation conducted in United Kingdom and United States suggested no association between increased age and CBS. It affects elderly only due to increased incidence of eye disease such as macular degeneration, glaucoma, diabetic retinopathy, cataracts etc. in geriatric population and can affect people of all ages It was also observed to be caused by a lack of sensory information. When there is lack of information from the eye to the brain due to any eye disease, the brain creates hallucination to fill this gap of information. It can also be caused by changes in the activity of brain regions or alterations in neurotransmitter system. Differentiating Charles Bonnet syndrome from other Diseases

CBS must be differentiated from other diseases that cause hallucinations such as:  Lewy Body Dementia  Parkinson's Disease Psychosis  Schizophrenia: Epidemiology and Demographics Their meta-analysis showed a pooled prevalence of CBS in low vision patients of 19.7% (95% CI: 13.8–26.4%). Age  Patients of all age groups may develop CBS.  CBS is more commonly observed among the elderly most commonly with age over 64 due to increased incidence of eye diseases. Gender  A study conducted in the Netherlands found that 6 out of 7 patients of CBS were women. Risk Factors  Common risk factors in the development of CBS are acquired visual impairment and social isolation. Natural History, Complications and Prognosis  Patients with Charles Bonnet Syndrome (CBS) remain asymptomatic for many years.  Early clinical symptoms include the onset of vivid visual hallucinations, often involving complex scenes, people, or patterns.  Patients with CBS may sometimes suffer from depression thinking something is wrong with their mental health.  Common complications of CBS include anxiety or distress related to the hallucinations.  The prognosis is generally good, and the long-term mortality rate of patients with CBS is low

 Diagnosis Diagnostic Criteria  The diagnosis of CBS is made after a thorough evaluation by gaining medical history, evaluating visual condition and conducting a physical examination History and Symptoms  CBS involves hallucinations of different types and frequency  Some experience hallucinations of simple shapes, colors, and patterns while others hallucinate of objects, things, people animals etc.  Some experience hallucinations regularly while others hallucinate irregularly Physical Examination  Patients with CBS are mentally healthy individuals with usually no neurological conditions.  Physical examination of these patients includes neurological assessment to find out if the main cause of hallucination is some neurological condition or just CBS. Visual Assessment This condition is mainly caused by visual impairment and many cases have reported a decrease in hallucination with improved visual acuity. Visual assessment is said to be the most important assessment for the diagnosis of CBS. Laboratory Findings  There are no specific laboratory findings that are specifically conducted for the assessment of CBS CT scan or MRI For now, Typical diagnosis does not involve any CT scan or MRI until there are strong symptoms of other neurological conditions. Other Diagnostic Studies There are no other diagnostic studies associated with CBS Treatment Medical Therapy  Medication to improve vision acuity can help reduce hallucinations.  In case of severe hallucinations certain medications such as antiepileptic and antipsychotics can be given.  These medications are avoided in acute cases because of their potential side effect.  When given these medications, patients are monitored closely for the adverse events.

Surgery

 No surgery can be performed to reduce hallucination until it is done to reduce visual impairment or visual damage. Emotional support:  The main area of focus for patients with CBS is to provide them with emotional support. And let them know that these hallucinations are not related to their mental condition but it is due to their visual impairment. These patients encounter mental stress thinking something is wrong with their mental health and the improvement in distress can be seen when they are provided with emotional support. Prevention  There are no primary preventive measures available to prevent oneself from hallucination but visual acuity should be monitored closely so that no visual loss/ impairment/ damage can lead to the extent where hallucinations begin.