In vivo mapping of incremental cortical atrophy from incipient to overt Alzheimer's disease.

Progressive brain atrophy is believed to be the Alzheimer's disease (AD) marker with the greatest evidence for validity. Mapping the topography of cortical atrophy throughout the stages of severity may allow the neural networks affected to be identified. Twenty healthy elderly persons (OH, MMSE 29.1 +/- 1.0), 11 patients with incipient AD (iAD, 26.5 +/- 2.0), 15 with mild AD (miAD, 23.5 +/- 2.2), and 15 with moderate AD (moAD, 16.5 +/- 2.0) underwent 3D magnetic resonance. Cortical pattern matching analysis was performed and maps of percent differences in gray matter distribution were computed between the following groups: iAD versus OH, miAD versus iAD, and moAD versus miAD. Compared to OH, iAD patients exhibited a mean cortical gray matter loss of 9-20% in areas encompassing the polysynaptic hippocampal pathway (posterior cingulate/retrosplenial and medial temporal cortex) and subgenual/orbitofrontal cortices, and a less widespread loss of 5-11% in other neocortical areas. Compared to iAD, miAD featured widespread mean gray matter loss of 14-19% in areas encompassing the direct hippocampal pathway (temporal pole, temporoparietal association cortex, and dorsal prefrontal cortex), sensorimotor, and visual cortex, with a less marked loss (7-9%) in the polysynaptic pathway areas. Compared to miAD, only atrophy in the primary sensorimotor cortex was still relatively marked in moAD, with a mean gray matter loss of 10-11%; the loss in other regions was generally below 10%. These findings suggest that the polysynaptic hippocampal pathway is affected in iAD, the direct pathway and sensorimotor and visual networks are affected in moAD, and the sensorimotor network is affected in moAD.