Early diagnosis of Alzheimer's type dementia with special reference to the clinicopathology of mild cognitive impairment

Abstract

A considerable number of patients with Alzheimer‐type pathology begin with various types of psychiatric symptoms. In discussing mild cognitive impairment (MCI) and Alzheimer‐type dementia (ATD), psychiatric symptoms other than memory impairment must be considered. There is no obvious neuropathological boundary that distinguishes dementia from non‐dementia. In fact, although Alzheimer‐type pathology of MCI corresponds mainly to Braak's stage I or II, it has a wide range extending from Braak's stage I to V or VI. Difference in compensatory ability and environmental factors among individuals seem to affect the mental state more extensively than previously thought. MCI manifests most frequently in Braak's stage I and II (transentorhinal stage) and its Alzheimer‐type pathology is almost confined to the hippocampal region. Although the degree and distribution of senile plaques vary in each patient, the cerebral isocortex is virtually free from degeneration. There is discrepancy between the corresponding neuropathology and hypo‐metabolism in the posterior cingulated cortex (PCC), which is regarded as an important finding for the early diagnosis of ATD. In PCC, hypo‐metabolism seems to precede that morphological change especially in its premorbid or early period of ATD. The state of MCI could also occur in other diseases causing dementia, among which tangle‐only dementia is particularly notable. The characteristic of tangle‐only dementia is the gradually progressive, persistent pathological memory impairment with relative preservation of personality and cognitive function. These characteristics meet the criteria for MCI. Thus, tangle‐only dementia should be taken into account in patients who exhibit MCI but do not progress to the development of dementia over a prolonged period.