Background. Temporal lobe atrophy on magnetic resonance
imaging (MRI) has been suggested as
a specific diagnostic marker for Alzheimer's disease (AD). No previous
comparison with dementia
with Lewy bodies (DLB) has been reported.
Method. T1-weighted MRI scans were performed on 11 subjects
with AD (nine with
NINCDS/ADRDA probable AD and two with neuropathologically proven AD)
and nine subjects
with DLB (four with probable DLB diagnosed by clinical criteria and five
with neuropathologically
proven DLB). Groups were matched for age, duration of illness and cognitive
test score. Two raters,
blind to diagnosis and neuropathological findings, measured the volumes
of the frontal lobes,
temporal lobes, hippocampi, parahippocampal gyri, amygdalae, and caudate
nuclei using a
computerized volumetric analysis system. Scans were also rated for medial
temporal atrophy on a
four-point scale by an experienced rater.
Results. AD subjects had significantly smaller left temporal
lobes and parahippocampal gyri than
those with DLB. Medial temporal atrophy was present in 9/11 AD cases
(82%) and absent in 6/9
(67%) of DLB cases. Two neuropathologically confirmed cases of DLB had
severe medial temporal
atrophy; both had concurrent AD-type pathology in the temporal lobe (Braak
stage 4).
Conclusions. This pilot study supports the hypothesis that
a greater burden of pathology centres on
the temporal lobes in AD compared with DLB, except in DLB cases with concurrent
Alzheimer
pathology. A larger study is needed to confirm these findings and to determine
whether MRI has
a role in assisting with the clinical differentiation between DLB and AD.