The effect of brain atrophy on cerebral hypometabolism in the visual variant of Alzheimer disease.
BACKGROUND
Brain glucose metabolic rates measured by positron emission tomography can be more affected by partial volume effects in Alzheimer disease (AD) than in healthy aging because of disease-associated brain atrophy.


OBJECTIVE
To determine whether the distinct distribution of cerebral metabolic lesions in patients with the visual variant of AD (AD + VS) represents a true index of neuronal/synaptic dysfunction or is the consequence of brain atrophy.


METHODS
Government research hospital.


METHODS
Resting cerebral metabolic rate for glucose was measured with positron emission tomography in a cross-sectional study of AD and AD + VS groups and in healthy control subjects. Segmented magnetic resonance images were used to correct for brain atrophy.


METHODS
Patients with AD + VS had prominent visual and visuospatial symptoms. There were 15 patients with AD, 10 with AD + VS, and 37 age-matched control subjects.


METHODS
Measurement of the rate of cerebral glucose metabolism.


RESULTS
Before atrophy correction, the AD + VS group, compared with the control subjects, showed hypometabolism in primary and extrastriate visual areas and in parietal and superior temporal cortical areas. Compared with the AD group, the AD + VS group showed hypometabolism in visual association areas. After atrophy correction, hypometabolism remained significantly different between patients and controls and between the 2 AD groups.


CONCLUSIONS
The reductions in cerebral hypometabolism represent a true loss of functional activity and are not simply an artifact caused by brain atrophy. The different patterns of hypometabolism indicate the differential development of the lesions between the AD and AD + VS groups.
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA.
A L
AL
Bokde
P
P
Pietrini
V
V
Ibáñez
M L
ML
Furey
G E
GE
Alexander
N R
NR
Graff-Radford
S I
SI
Rapoport
M B
MB
Schapiro
B
B
Horwitz
D000368:Aged; D000544:Alzheimer Disease / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology*; D001284:Atrophy; D004734:Energy Metabolism; D005260:Female; D005625:Frontal Lobe / Q000378:metabolism / Q000473:pathology; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010296:Parietal Lobe / Q000378:metabolism / Q000473:pathology; D013702:Temporal Lobe / Q000378:metabolism / Q000473:pathology; D014055:Tomography, Emission-Computed; D014793:Visual Cortex / Q000378:metabolism* / Q000473:pathology*
D005947:Glucose