VISUAL HALLUCINATIONS IN AN ELDERLY WOMAN: A PRESENTATION OF CHARLES BONNET SYNDROME?

Abstract

To the Editor: The patient was an 81-year-old African-American woman with hypertension, hyperlipidemia, visual loss secondary to retinitis pigmentosa, and cataracts status post bilateral iridectomy. Over the previous 3 years her vision had steadily decreased, and she was legally blind. In tandem with her decrease in vision was the occurrence of visual hallucinations, not associated with memory deficits. There was no psychiatric history, paranoid ideations, auditory hallucinations, depression, or anxiety. The visual hallucinations occurred primarily at night, often awakening her from sleep. They worsened with stress and decreased in intensity with rest and were frightening to the patient. There were no reports of headaches, dizziness, or shortness of breath. The rest of the review of systems was unremarkable. Examination included an infusion computed tomography scan of the brain, carotid Doppler, and magnetic resonance angiograms, which were negative. A full metabolic panel, including a complete blood count, electrolytes, glucose level, thyroid function, red blood cell folate, B12, and liver function studies, were normal. Visual hallucinations, which take the form of patterned straight lines or detailed pictures of people, animals, or buildings characterize the Charles Bonnet Syndrome (CBS).1, 2 The imagery can be enjoyable, frightening, and sometimes upsetting. It occurs more commonly in older people and in those with significant vision loss and in bilateral versus unilateral ocular disease. The first manifestation of CBS typically occurs after a period of sudden worsening of vision and may disappear spontaneously through maneuvers such as eye closure.3 First described by Swiss philosopher Charles Bonnet in 1760, triggers of the syndrome include fatigue, low levels of illumination, bright lighting, and stress (as with this patient).4 Once manifested, the images may last for periods varying from seconds to minutes to hours. Although identified more than 2 centuries ago, CBS remains poorly understood and is often misdiagnosed in the clinical setting.5 Patients experiencing CBS are reluctant to advise their physicians or family members for fear of being categorized as mentally ill. Although the most commonly associated ocular pathology is age-related macular degeneration, the syndrome has been associated with cataracts, glaucoma, diabetic retinopathy, and retinitis pigmentosa (as in this patient). Patients with CBS must have formed and complex persistent or repetitive visual hallucinations, full or partial retention of insight (awareness of the unreal nature of the hallucination), absence of delusions, and absence of auditory or other sensory hallucinations.2, 6 The root cause of CBS remains elusive. One theory advances hyperexcitability of deafferented brain regions as a possible etiology for this syndrome, noting that these complex visual hallucinations are typically seen in the setting of visual deterioration from ocular pathology, such as retinitis pigmentosa.7, 8 It is theorized that deafferentation occurs shortly after lesions occur within the retinal or visual pathways; surviving neurons attempt to recover and adapt to the decline in visual afferent input by altering their sensitivity to stimuli. Because these surviving neurons exhibit hypersensitivity to residual visual stimuli during this adaptive period, hallucinations may still result when they are exposed to normal incoming visual stimuli. Although decreased visual stimulation is believed to predispose individuals to CBS, persons who are completely blind rarely experience these hallucinations.4 Therefore, it is believed that it is during acute periods of acute or dynamic lowered visual acuity rather than during chronic or static impairment that an increased incidence of CBS is seen.9 Differential diagnoses include thalamic or brainstem lesions, Parkinson's disease, Lewy Body Dementia, migraine, schizophrenia, epilepsy, and hallucinogenic induced states. Drugs such as gabapentin have been prescribed to treat CBS with measured success. Gabapentin's mechanism of action is believed to be related its effect on brain pathways involved in seizure pathology. Patient education and counseling have resulted in the most significant success, as patients learn that the syndrome does not represent mental disorder. Our patient presented a classic case of CBS. As primary providers of care to older people, geriatricians are uniquely positioned to determine the existence of CBS and to exclude other competing diagnoses. As part of the routine geriatric evaluation, all elderly patients with ocular disease should be queried about visual hallucinations. With accurate diagnosis of this syndrome, geriatricians will help to alleviate the high levels of resultant anxiety and through empathic patient education, seniors will be taught about the benign nature of the syndrome and will be given adaptive techniques that will help them to enjoy a good quality of life. Financial Disclosure: None. Author Contributions: June M. McKoy and Laura McGartland identified the case in clinic, contributed to the original idea, acquisition of subject's data, and preparation and editing of the material. Sponsor's Role: None.