[Degenerative dementia of the oldest old]

We investigated seven brains from patients 99-105 years of age with a clinical diagnosis of Alzheimer-type dementia (ATD). The pathological findings were as follows. 1) These cases could be divided into two groups: cases with localized cortical atrophy in the medial part of the temporal lobe, and a case with diffuse atrophy in the cerebral cortex. Atrophied cortex in both groups showed laminar degeneration consisting of neuronal loss, neuropil loosening and astrocytosis resulting in fibrillary gliosis, which was particularly marked in the 2nd and 3rd layers of the cerebral cortex. In contrast, the structure of the six cortical layers was preserved when there was no laminar degeneration. Laminar degeneration correlated with cortical atrophy. 2) Cases with localized atrophy were further divided into two groups: group 1 (4 cases) showed small numbers of senile plaques (SPs) and large numbers of neurofibrillary tangles (NFTs' in CA1 of the hippocamupus, subiculum, and parahippohcampul gyrus, while group 2 (2 cases) showed widespread and numerous SPs and NFTs in the cerebral cortex. The distribution of SPs and NFTs in group 2 was similar to that of the case (group 3) with diffuse cortical atrophy. It was considered that group 2 was limbic type ATD and that group 3 was neocortical type ATD, because both groups met our pathological diagnostic criteria ATD. In contrast, group 1 could not be regarded as ATD because the numbers of SPs and NFTs were below those found in ATD, even though this group showed laminar degeneration the same as that of groups 2 and 3. It therefore is likely that group 1 is a unique type of degenerative dementia, pathogenetically different from ATD.