Reappraisal of the fine structure of Alzheimer's neurofibrillary tangles.

Alzheimer's neurofibrillary tangles were studied by electron microscopy. The study includes four cases of Alzheimer's disease, two cases of atypical senile dementia, and one case of progressive supranuclear palsy. In Alzheimer's disease the tangles were composed of either straight filaments or paired helical filaments. In progressive supranuclear palsy the tangles were composed of 15 nm straight filaments or helical filaments. A few straight filaments were mixed with paired helical filaments. In atypical senile dementia, both straight and paired helical filaments comprised the tangles and one type of filaments appeared to intermingle with the other in the same neurons.