A Study in Charles Bonnet Syndrome

When a patient’s chief complaint involves visual hallucinations, practitioners may be quick to assume that the underlying disease process is rooted in psychiatric illness. But one condition, known as Charles Bonnet Syndrome (CBS), typically presents with visual hallucinations – and it is directly caused by long-standing, ocular disease.

Although CBS is typically associated with age-related macular degeneration (AMD) and elderly patients, this condition is not exclusive to either AMD or the elderly. Instead, the development of CBS is rooted in the severity of visual impairment irrespective of age.

Though different theories exist concerning the pathophysiology of CBS, the most widely accepted explanation is that a severe reduction in visual acuity causes deafferentation of the visual sensory pathway and subsequent disinhibition of the cortical regions of the brain that affect vision (2). fMRI studies of patients with CBS support this theory, revealing the presence of activity in the ventral occipital lobe and visual cortical regions during episodes of hallucination (3).

For practitioners, understanding the experience of patients with this CBS is of utmost importance. It is estimated that only 15 percent of patients with CBS will ever admit to their healthcare provider that they experience hallucinations due to a fear of being diagnosed with mental illness or dementia (6).

Here, we present a case that may help clinicians better understand the clinical features of CBS.

A CBS case study
 

A 96-year-old woman with a past medical history of AMD, hypothyroidism, hypertension, multiple hospital admissions for UTI’s, and no past psychiatric history presented to the emergency department with altered mental status (AMS) and visual hallucinations.

The patient’s primary care provider contacted EMS upon noticing that the patient was displaying behaviors which differed from baseline. Of note, the patient was taking longer than usual to answer questions and seemed to be acting out of character. In the ED, her labs, urinalysis, chest x ray, and head CT were all within normal limits. She was admitted to the medical floor for further diagnostic clarification.

After admission, she revealed to the medical team that she was first diagnosed with AMD around 50 years ago. Throughout the past several decades, her visual acuity had deteriorated. At the time of exam, she was only able to count fingers and roughly make out shapes.

Her first visual hallucinations began approximately 10 years ago. The hallucinations occur on a weekly basis and do not appear to be dependent on the time of day. While her hallucinations initially elicited distress and confusion, she has since learned that they are not real and she has become largely unbothered by them.

When discussing the content of these visual hallucinations, the patient stated that she often sees family members, animals, and “things people see in everyday life.” She also added that, while these hallucinations are usually visual, they occasionally contain an auditory component which contextually supplements the imagery.

The patient denied any history of psychiatric disorder, prior psychiatric hospitalization, or outpatient psychiatry visits, but stated that she was previously taking Ativan as prescribed for anxiety. She denied any family history of mental illness and denied any use of tobacco, alcohol, marijuana, or other illicit substances. Her mental status exam showed no evidence of preoccupation with internal stimuli, was negative for obvious delusions or paranoia, and was otherwise unremarkable.

Subsequent referral to neurology confirmed visual and auditory impairment. Furthermore, she was found to be neurologically intact – making the diagnosis of a neurodegenerative disease unlikely. The neurology team concluded that the hallucinations were likely due to CBS. The patient was recommended to follow up with her ophthalmologist as an outpatient and she was subsequently discharged.

Intervention, treatment, and takeaways
 

Though the presence of auditory hallucinations typically rules out CBS, our patient experienced auditory hallucinations exclusively in the context of sepsis and only her visual hallucinations were chronic. Given the non-distressing nature of her hallucinations, our patient disclosed that she did not want to start any psychotropic medications.

There is currently no specific, agreed-upon treatment for CBS other than treating the underlying cause of vision impairment (7). Despite this, some case studies report success with using a low dose of risperidone and valproate (8). Other reports showed improvement with SSRIs as well as Clonazepam and Gabapentin (9). One control trial demonstrated reductions in frequency of hallucinations in CBS with transcranial direct current stimulation (10).

While the choice of pharmacological treatment remains open for debate, patients can still make meaningful improvements in their hallucinations. Because it is known that patients are more likely to experience CBS hallucinations when in settings of low light and low stimulation, patients must be encouraged to participate in activities that stimulate their mind. This may include participating in social activities, remaining active in the community, and occupying the brain with other stimuli, such as board games or crafts.

Ultimately, it is important that both patients and healthcare providers understand that this condition is not a neurodegenerative disease or a psychiatric illness. Further education is needed so that ophthalmologists can recognize and treat CBS. We hope that this article can add to that education.

Funding
 

The authors did not obtain funding for this case report. The authors have no financial interests to disclose.

Ethical approval
 

Patient provided consent for authorization of this case report.