The curious case of an invisible dog: a patient with non-psychiatric visual hallucinations

A 74-year-old man reported experiencing hallucinations of a dog standing on his right side, following a recent episode of infective endocarditis. There was no history of reduced conscious level, psychosis or substance misuse. Neurological examination revealed an isolated right inferior quadrantopia, and the hallucinations were visible only in the area of the visual defect. A computed tomography scan confirmed a left occipital lobe infarct, congruent with the clinical signs. The infarct was deemed to be have originated from a septic embolus of his infected aortic valve and he was diagnosed with Charles Bonnet's syndrome (CBS). CBS is characterized by the presence of stereotyped visual hallucinations on a background of partial sight and in the absence of any psychotic illness. Early recognition can prevent wrongful diagnosis of a psychiatric condition, which may provide comfort to patients. Management is centred on reassurance and counselling, with medical therapies reserved only for patients experiencing distressing hallucinations.