VISUAL HALLUCINATIONS IN AN ELDERLY WOMAN—WAS IT REALLY CHARLES BONNET SYNDROME?

Abstract

To the Editor: We read with interest the report by Drs. McKoy and McGartland describing visual hallucinations in an elderly woman.1 Their patient had several ocular conditions that are known to be associated with Charles Bonnet syndrome (CBS)—retinitis pigmentosa, cataracts, and, possibly, angle-closure glaucoma (as evidenced by the bilateral iridectomies). In addition, the patient was elderly, with bilateral poor visual acuity, both of which are risk factors for the development of CBS.2–4 The authors stated that the hallucinations “occurred primarily at night, often awakening her from sleep.”1 We feel that it is important to consider possible differential diagnoses of hallucinations that awaken a patient from sleep. A MEDLINE search revealed no references to cases of CBS when the hallucinations experienced were primarily those that awaken patients from sleep. Hallucinations that occur during periods of sleep may be hypnopompic or hypnagogic in nature. Hypnopompic and hypnagogic hallucinations are vivid, dreamlike hallucinations that occur as one is waking up or falling asleep, respectively (i.e., during sleep–wake transitions). These hallucinations are a differential diagnosis of, but distinct from, CBS.3,4 Manford et al. discussed some common differential diagnoses in a comprehensive review on complex visual hallucinations.5 They pointed out that normal consciousness is characteristic of CBS, whereas hypnagogic hallucinations occur when the patient is drowsy. Hypnopompic or hypnagogic hallucinations may occur in normal individuals and can sometimes be mistaken for CBS.3 In a community survey of 4,972 people aged 15 to 100 in the United Kingdom, 37.0% reported experiencing hypnagogic hallucinations, and 12.5% reported hypnopompic hallucinations.6 To determine the exact nature of the hallucinations in this patient, it would be useful to know additional details of the hallucinations experienced, including whether the patient experienced hallucinations during periods when she was fully awake, whether her eyes were open at the time of the hallucinations, and whether these hallucinations differed in any way from those that occurred during periods of sleep–wake transitions. In our experience investigating and treating patients with CBS, we have often found it difficult to definitively diagnose CBS if the hallucinations occurred primarily during periods immediately before or after sleep. We therefore restrict our diagnosis of CBS to patients who have a clear history of hallucinations occurring when they are fully awake. We agree with the authors that CBS is often underdiagnosed. Patients often do not volunteer their symptoms because of a fear of being labeled “insane” or a “psychiatric patient.”3,4,7 Some patients are bothered by their hallucinations and react negatively (fear or anger), as did this patient. Often, many are relieved to discover the benign nature of their hallucinations and that they are not “insane.”2–4 The prevalence of CBS ranges from 0.4% to 13% in different studies, depending on the study population.3,4,8 Because CBS is more common in elderly patients, and the prevalence of various sight-threatening ocular conditions increases rapidly with age, geriatricians have an important role in screening for CBS. In many cases, all that is needed is a sympathetic explanation of the benign nature of the condition, but it is important to exclude, as the authors have done, other systemic causes of hallucinations that may require treatment. Financial Disclosure: Neither author has any financial or proprietary interest in the subject of this letter. The authors did not receive any funding in the conduct of this research. Author Contributions: Dr. Tan and Dr. Au Eong contributed to the original idea and prepared and edited the letter. Sponsors' Role: None.