Can PET Distinguish AD from Vascular Dementia?
Independently of clinical history and evaluation and of CT or MRI, PET (like SPECT, see below) cannot easily distinguish AD from vascular dementia. Both syndromes demonstrate global reductions in brain metabolism and flow in relation to dementia severity (22), as well as heterogeneity of cognitive and local metabolic deficits. Large asymmetric metabolic or flow reductions that correspond to CT or MRI abnormalities, or reductions in the basal ganglia or thalamus, suggest vascular dementia, whereas sparing of primary as compared with association cortical areas suggests AD (3). Neither AD nor vascular dementia is accompanied by an elevated rOER (22). However, prior to the appearance of dementia in some subjects with leukoaraiosis and hypertension (a major risk factor for vascular dementia), rOER can be elevated (77). Recently, PET demonstrated that the rCBF response to hypercapnia is normal in AD but defective in vascular dementia of the Binswanger type (46).
