Characteristics of Alzheimer's Disease and Mild Cognitive Impairment Influenced by the Time of Onset.

Introduction: Although the prevalence of Alzheimer's disease (AD) is higher in older people compared to younger people, dementia has also been documented in younger adults. Although early-onset dementia and late-onset dementia had been considered a single disease in pathological investigations, many studies revealed differences in cognitive and neuroimaging changes between them. We evaluated differences in cognitive and neuroimaging changes among the following groups: individuals with early-onset AD (EOAD), late-onset AD (LOAD), early-onset mild cognitive impairment (EOMCI), or late-onset MCI (LOMCI), and healthy controls (HCs).

Methods: Patients underwent both a 1.5 Tesla magnetic resonance imaging scan and the Mini-Mental State Examination (MMSE). Differences in regional gray matter volumes and MMSE subscales were investigated among the five diagnostic groups.

Results: Compared to the EOAD group, the LOAD group had significantly higher scores on orientation in place. Compared to the LOMCI patients, the EOMCI patients achieved significantly higher recall scores. The LOAD and LOMC groups showed significant volume reductions in bilateral medial temporal regions compared to the HCs. The EOAD and EOMCI groups did not show significant atrophy of the medial temporal region compared to the HC group.

Conclusions: The hippocampal volume and memory were preserved in the patients with EOMCI or EOAD compared to those with LOMCI or LOAD. These findings may indicate that the distinct and differing patterns of neuropsychological changes between EOAD and LOAD are also common in MCI, which is intermediate between normal cognition and AD.