Differing patterns of temporal atrophy in Alzheimer’s disease and semantic dementia

Abstract

Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.

Anatomical and functional alterations in semantic dementia: A voxel-based MRI and PET study

“…The findings of our MRI study highlight, as expected, significant GM reduction in the left temporal neocortex (temporal pole, and inferior, middle and superior temporal gyri), and at a lesser degree, in the right temporal neocortex, in accordance with previous quantitative volumetric [7,22,39] and VBM [4,25,26,29,49] studies. This pattern of results is in agreement with the severe semantic memory deficits in our group of SD patients.…”

“…The GM reduction was also found to concern at a lesser degree the left fusiform gyrus, consistently with previous studies in SD [22,26,49], as well as in the amygdala, parahippocampal gyrus and hippocampus, predominantly on the left hemisphere. Left amygdala atrophy in SD has recently been shown in VBM [4,25] and in volumetric [39,78] MRI studies, and seems to be more pronounced than in Alzheimer"s disease.…”

“…Some studies have shown atrophy in other brain regions, notably the frontal lobes [39,49,64,69] and the amygdala [4,7,22,39,49,64,78]. It is worth noting that, with the evolution of the disease, SD patients develop executive dysfunction and behavioural symptoms [18], in accordance with the role of the frontal lobes in behaviour regulation.…”

“…Some authors [29,9] did not find significant atrophy of the hippocampus and adjacent structures using the SPM software which allows a voxel-by-voxel analysis (Voxel Based Morphometry, VBM) of the entire brain. Nevertheless, some studies using the region-of-interest (ROI) method [7,12,22,52] emphasized bilateral hippocampal atrophy, predominant on the left hemisphere. According to Chan et al [7] and Galton et al [22] the failure to identify hippocampal abnormality using VBM possibly reflects the limited resolution of the voxel-by-voxel method for small complex structures such as the hippocampus.…”

“…Nevertheless, some studies using the region-of-interest (ROI) method [7,12,22,52] emphasized bilateral hippocampal atrophy, predominant on the left hemisphere. According to Chan et al [7] and Galton et al [22] the failure to identify hippocampal abnormality using VBM possibly reflects the limited resolution of the voxel-by-voxel method for small complex structures such as the hippocampus. Indeed, this technique implies an automated comparison of individual data normalized on a template obtained from normal young control MRI scans, which is not optimal while considering demented patients with atrophied brains.…”