Brain 18F-FDG PET is known to have a good negative predictive value in the search for a neurodegenerative origin to cognitive disorders. Indeed, a ratio of 0.1 on the occurrence of worsening cognitive disorders has been reported in case of normal brain FDG PET.~However, in patients without cognitive complaints, the risk of developing objective cognitive impairment is estimated to be 8% per year and the risk of developing dementia in patients with mild cognitive impairment 22% per year.~Brain 18F-FDG PET is a prognostic factor for the occurrence of MCI or for the conversion of MCI to Alzheimer's disease , but we do not really know the impact on the longer-term occurrence of cognitive impairment in patients with a normal brain 18F-FDG PET.~Also, it is commonly accepted that a normal brain 18F-FDG PET scan can rule out a neurodegenerative origin for cognitive impairment.~However, the detection sensitivity of brain 18F-FDG PET is about 90% . Furthermore, we do not know the pathophysiological factors that cause false negative PET scans and it would be interesting to study them (age, sex, medical history, results of neuropsychological tests, etc.).~Based on subjects available freely on the internet, an American team showed that brain 18F-FDG PET was predictive of cognitive decline in subjects with no or minor cognitive disorders.~Only a longitudinal study will allow to really know the true negative predictive value of a normal 18F-FDG PET scan and the factors associated with a risk of dementia in these subjects. This will allow us to better understand the prognostic impact of a normal brain 18F-FDG PET scan and to identify a subpopulation that remains at risk, including in case of normal brain 18F-FDG PET.
Brain 18F-FDG PET (positron emission tomography) is recognised as having a good negative predictive value in the search for a neurodegenerative origin of cognitive disorders. Indeed, a ratio of 0.1 on the occurrence of worsening cognitive disorders has been reported in case of normal brain FDG PET.~However, the risk of developing objective cognitive disorders in patients with no cognitive complaints is estimated at 8% per year and the risk of developing dementia in patients with mild cognitive disorders at 22% per year.~Cerebral 18F-FDG PET is a prognostic factor for the occurrence of unusual clinical manifestations (MCI) or the conversion of MCI to Alzheimer's disease, but we do not really know the impact on the longer term occurrence of cognitive impairment in patients with normal cerebral 18F-FDG PET.~Only a longitudinal study will allow us to really know the true negative predictive value of a normal 18F-FDG PET scan and the factors associated with a risk of dementia in these subjects. This will allow us to better understand the prognostic impact of a normal brain 18F-FDG PET scan and to identify a sub-population that remains at risk, including in the case of normal brain 18F-FDG PET.