69. LOST IN THE SILENCE: A CASE OF AUDITORY CHARLES BONNET SYNDROME AND COGNITIVE DECLINE

Introduction

Charles Bonnet syndrome (CBS) is an isolated visual pseudohallucinatory phenomena in the setting of visual impairment with preserved insight and lack of other psychiatric diagnoses. This rare condition was identified originally in 1938 by de Morsier [1], later expanded to include atypical cases of CBS in which auditory hallucinations develop following hearing impairment rather than the more common visual hallucinations [2,3]. While some reports have hinted at connections between CBS and the development of dementia, few cases of auditory CBS have been published in the setting of cognitive impairment [4,5].

Methods

Ms. S is a 75 year old female with no prior psychiatric history who suffered progressive hearing loss requiring hearing aids in her late 60s. At age 70, she began to experience auditory phenomena where she would hear music and conversations from next door that were not present. These auditory hallucinations were accompanied by the development of paranoid and persecutory delusions. By her early 70s, Ms. S had multiple inpatient psychiatric hospitalizations and had been trialed on many psychotropic agents with only modest improvement. These hallucinations would often initially remit while in the hospital, only to return at home. After three years of persistent auditory symptoms, Ms. S began to exhibit motor symptoms including gait instability, fine tremor, and stooped posture. Shortly after, she began exhibiting word finding difficulties and further cognitive decline including difficulty completing instrumental activities of daily living.

Brain Magnetic Resonance Imaging (MRI) was notable for moderate global atrophy and mild chronic cerebrovascular disease burden, but etiology of Ms. S’s cognitive impairment remained inconclusive. Dopamine transporter (DaT) Scan, alpha-synuclein dermal punch biopsy, Fludeoxyglucose-18 (FDG) Positron Emission Tomography (PET) scan and neuropsychiatric testing were unable to further identify a specific neurological diagnosis.

During her last inpatient psychiatric admission, Ms. S was started on a low dose of oral olanzapine in addition to a rivastigmine transdermal patch which was found to eliminate delusional content though intermittent auditory phenomenon remained. At discharge, Ms. S reported she was no longer bothered by the voices and music, and understood that they were likely related to her hearing loss.

Results

Auditory CBS may affect up to 2.5% of elderly individuals with hearing loss [6]. Isolated case reports have shown a possible connection between auditory CBS and cognitive impairment, though research in this area is lacking [3]. While there are no controlled trials in CBS, case studies have indicated reassurance as a main treatment modality, though this is notably more challenging in the setting of memory impairment [3]. Olanzapine, pregabalin, clonazepam, and acetylcholinesterase inhibitors have also been mentioned as possible treatment options, similar to interventions we used in Ms. S’s case [3,4]. Additionally, some studies suggest that increasing acoustic stimulation and social engagement may be beneficial for individuals with auditory CBS [4]. This may explain why Ms. S’s symptoms improved in the noisy hospital environment but worsened when she was alone at home.

One possible mechanism explaining the relationship between hearing loss, auditory hallucinations, and cognitive impairment suggests that abnormal protein deposition associated with neurodegenerative pathology may disrupt connections within auditory pathways, lowering the threshold for spontaneous activity of the auditory association cortex [5]. While the exact etiology behind Ms. S’s cognitive presentation remains unclear, the timeline of her auditory phenomenon and response to interventions aligns with the characteristics of auditory CBS. In those with hearing loss, motor symptoms, and cognitive deficits, the addition of auditory hallucinations adds to the burden of disease. More research is warranted to better understand this connection in order to develop more targeted workup and treatment for those with auditory CBS.

Conclusions

This case highlights the potential association between auditory Charles Bonnet syndrome, hearing loss, and cognitive decline, emphasizing the need for further research to elucidate underlying mechanisms and develop targeted interventions.