Temporal lobe rating scale: application to Alzheimer's disease and frontotemporal dementia

Objectives-Temporal lobe atrophy as assessed by MRI can be measured in seve ral ways. Volumetric measurements are quantitative but very time consuming and require extensive training to perform, so are not easily transferable t o clinical practice. Visual rating scales, by contrast, are quick and widel y applicable. Although medial temporal lobe atrophy is well described in Al zheimer's disease (AD), it is uncertain how early these changes can be dete cted and whether they discriminate AD from other neurodegenerative diseases , most notably frontotemporal dementia (FTD). The objectives were (1) to de velop a widely applicable temporal lobe rating scale, and (2) to characteri se and quantify the patterns of temporal lobe atrophy in AD versus temporal and frontal variants of FTD. Methods-The temporal lobe assessments were made using an established hippoc ampal rating scale extended to incorporate additional temporal regions. Thi s was firstly validated with volumetric analysis and then applied to 30 pro bable AD, 30 FTD (consisting of 17 temporal variant (semantic dementia) and 13 frontal variant) and 18 control coronal MRI images. Results-Bilateral hippocampal atrophy was found in 50% of the patients with AD. Contrary to expectations, patients with semantic dementia also had hip pocampal atrophy, which for the left side exceeded that seen in AD; other r egions (temporal pole, parahippocampal gyrus, and lateral temporal lobe), s pared in AD, were severely atrophied in this group. The patients with front al variant FTD occupied an intermediate position and were largely indisting uishable from AD. Conclusions-Hippocampal atrophy is, therefore, not specific for AD. Semanti c dementia can be distinguished from AD, by the presence of severe bilatera l atrophy of the temporal pole, parahippocampal and lateral regions. These bindings have implications for the differential diagnosis of dementias.