FDG is 2-fluorodeoxyglucose, which is an analogue for glucose. Its uptake by neurons reflects the metabolic activity in an anatomic region. The pattern of change seen on the scan parallels changes seen on histology.
Indications for FDG-PET scanning in a patient suspected of having Alzheimer's disease:
(1) inability to differentiate from other forms of dementia, especially when there may be a mixed form
(2) very early cognitive impairment, to diagnose early and predict future prognosis
(3) monitoring response to therapy, especially in clinical trials
FDG-PET scan findings in a patient AD:
(1) bilateral hypometabolism of glucose (decreased uptake), which may be asymmetrical:
(1a) temporal and parietal cortex, which are affected more than the frontal lobes (there is relative sparing of the frontal lobes unless there is a mixed form of dementia or advanced AD)
(1b) posterior cingulate cortex
(1c) entorhinal cortex
(2) normal metabolism of glucose:
(2a) visual/occipital cortex
(2b) sensorimotor cortex
(2c) cerebellum
(2d) basal ganglia and thalamus
(2e) brainstem
