Objective: To investigate the specificity of atrophic changes in the corpus callosum (CC) compared with the cerebellum and pons in patients with Alzheimer Disease (AD), healthy elderly subjects (HE), and a sample of prospectively studied subjects who have developed cognitive decline or "incipient dementia" (ID).
Design: Cross-sectional comparison by age using quantitative MRI.
Setting: Ambulatory research unit.
Participants: Sixty HE subjects (mean age 78.2 years; range 66-95), 20 ID subjects (mean age 88.1 years; range 78-98) and 39 AD subjects (mean age 72.2 years; range 52-91) were enrolled in longitudinal studies of healthy aging or AD. The population was selected for optimal health; all were examined to exclude medical, neurological and psychiatric illness.
Measurements: Brain atrophy by quantitative MRI.
Results: AD subjects had smaller CC than HE or ID subjects, who did not differ from each other. All three sectors of the CC were smaller in AD than in HE or ID subjects. The cross sectional area of the cerebellum and pons did not differ between groups. HE and ID subjects showed a significant decline in CC size with age. No age-related decline was found for AD subjects. The regional atrophy of the CC in AD subjects was significantly related to cognitive function but not to disease duration.
Conclusions: Atrophy of the CC differentiates HE and ID from AD subjects and tracks the cognitive decline of this disease. In addition, optimally healthy subjects show an age-related decline in callosum size. The atrophy is specific to the CC, a cortical projection system, and does not occur in cerebellum or pons.