Complex visual hallucinations in Charles Bonnet Syndrome are associated with a hypermetabolism in the visual associative cortex

Introduction: Charles Bonnet Syndrome is a disorder characterised by complex visual hallucinations in the visually impaired patient. These hallucinations presumably arise from visual association cortical areas after being deafferentiated from the central visual pathway („deafferentiation theory“). Such deafferentiation typically occurs in eye-diseases such as macular degeneration or optic atrophy.

Case presentation: Here, we present a case of a 94 year old otherwise healthy woman who was brought to the emergency department with acute onset of visual disturbances such as macropsia and protosometamorphopsia (distorted faces). During these episodes a hemianopsia to the left side was observed. In a CT and MRI scan of the head a mild vasculopathic encephalopathy but no new ischemic lesion in the visual cortex could be seen. An Electroencephalography (EEG) did not show any focus or epileptiform discharges. In an ophtalomological examination a glaucomatic atrophy of both eyes could be diagnosed. For further evaluation a Fluor-Desoxy-Glucose-PET was performed which showed a local diminishment of glucose uptake in the right primary visual cortex (Brodman Area 17/18). In the adjacent visual associative area (BA 18/19) a local augmentation of glucose uptake was recognised going along with a hypermetabolism in this area.

With a glaucoma therapy the symptoms of our patient improved rapidly and she was dismissed without symptoms.

Conclusion: The observed hypermetabolism in the visual associative areas is most likely responsible for the patient's visual hallucinations and the temporarily occurring visual field defects. Thus our findings support the deafferentiation theory: A hypometabolism in the primary visual cortex which can arise from many eye diseases can cause a lack of sensory input into the visual associative cortex and thus may lead to consecutive neuronal discharges in this area leading to complex visual hallucinations. These pathophysiological processes can be visualised as hypermetabolism in FDG-PET.