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.