Objective:
Because age of onset does not reliably define two subtypes of Alzheimer's disease, classification based on the severity of neuronal degeneration was tested.
Design:
Numbers of extracellular tangles and pyramidal neurons in the hippocampus were used to group patients.
Patients:
The study population consisted of 46 elderly patients satisfying DSM-III criteria for dementia and NINCDS-ADRDA criteria for definite Alzheimer's disease after death.
Results:
Univariate logistic regression analysis showed the numbers of neurofibrillary tangles and pyramidal neurons and the duration of dementia were significantly as- sociated with grouping based on the presence of abundant extracellular tangles. Ninety-one percent of patients were correctly classified as compared with 85% correctly classified by age of onset data. Odds ratios showed that increasing numbers of neurofibrillary tangles predicted greater severity of neuronal loss.
Conclusion:
The results of the study indicate the importance of neurofibrillary degeneration, not the deposition of amyloid, in the pathogenesis of Alzheimer's disease. They support a classification of Alzheimer's disease related more closely to the severity of neurofibrillary degeneration than to age at onset.