Beyond the hippocampus: MRI volumetry confirms widespread limbic atrophy in AD

To examine volumetric changes in limbic structures in patients with probable AD using planimetric measures on MRI.

Limbic structures (i.e., hippocampus, amygdala, anterior thalamus, hypothalamus, mamillary bodies, basal forebrain, septal area, fornix, and cingulate, orbitofrontal, and parahippocampal cortices) were traced on 3D T1-weighted MR images of 40 patients with mild to moderate AD and 40 age-, sex-, and education-matched normal control subjects. Limbic volumes were compared between groups and the predictive ability was assessed.

Overall, limbic structures showed significant atrophy in AD patients compared with normal control subjects. Differences (p < 0.05) were found in all limbic regions except the anterior cingulate cortex. The greatest percentage volumetric losses occurred in the septal area (34%), hippocampus (28%), amygdala (21%), parahippocampal cortex (21%), and posterior cingulate cortex (20%). Combining volumetric measures of amygdala and septal area distinguished patients with AD from normal control subjects with 93% accuracy.

These results verify that system-wide limbic degeneration occurs in patients with AD. In addition, atrophy in selected limbic structures was used to distinguish patients with AD from normal elderly individuals with over 90% accuracy in this select clinical sample. The measures require further exploration in samples more representative of those seen by primary care physicians before their utility can be accurately assessed.