Déjà vécu with recollective confabulation: an unusual presentation of Alzheimer's disease.

A man in his 80s presented with gradual onset of a persistent and delusion-like perception that novel encounters are repetitions of previous experiences. Within 2 years of symptom onset, he had impaired verbal memory and executive dysfunction on neuropsychological assessment. Cerebrospinal fluid core Alzheimer's disease (AD) biomarkers analysis supported probable AD. Generalised and left temporal atrophy was seen on MRI of the brain. Neurological fludeoxyglucose-positron emission tomography (PET)/CT showed left temporal and bilateral frontal lobe hypometabolism. His presenting symptom is known as déjà vécu with recollective confabulation, a rare phenomenon associated with AD and other neurodegenerative disorders. While several potential mechanisms have been previously proposed, the fludeoxyglucose-PET/CT hypometabolism in the temporal and frontal lobes in this case suggests dual deficits in recognition memory and metacognition may be culprit mechanisms. Although uncommon, déjà vécu with recollective confabulation is a fascinating phenomenon that can provide a unique insight into memory and delusional processes in dementia.