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Differing patterns of temporal lobe atrophy in Alzheimer's disease and semantic dementia.
Galton, C.J., PATTERSON, K., GRAHAM, K., Lambon Ralph, M.A., Williams. G., Antoun, N., Sahakian, B.& HODGES, J.R.
Neurology, 57, 216-225
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Objective: To characterize and quantify the patterns of temporal lobe atrophy in Alzheimer's disease (AD) vs. semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia, SD) clinical studies suggest polar and infero-lateral temporal atrophy with hippocampal sparing, but quantification is largely lacking. Methods: A volumetric method for quantifying multiple temporal structures was applied to 26 probably AD, 18 SD patients and 21 matched control subjects. Results: We confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, SD patients had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the SD group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, while naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures. Conclusions: Hippocampal atrophy is not specific for AD but is also seem in SD. Distinguishing the SD patients was the seer global, but asymmetrical (left>right) atrophy of the amygdala, temporal pole, fusiform and infero-lateral temporal gyri. These findings have implications for the diagnosis and understanding the cognitive deficits in AD and SD.