Alzheimer's changes in non-demented and demented patients: a statistical approach to their relationships

The anterior hippocampus and the entorhinal cortex of 167 non-demented individuals (controls) and 22 patients with Alzheimer's dementia were investigated. Senile plaques and neurofibrillary tangles were counted on paraffin sections stained with methenamin silver and Gallyas silver iodide, respectively. The results showed that both senile plaques and neurofibrillary tangles areal densities (lesions per mm2) correlated significantly with age in the control collective. No significant correlation between Alzheimer's disease lesions and age was found in patients with Alzheimer's dementia. Positive and significant correlation between senile plaques and neurofibrillary tangles was found in the control group but not in the Alzheimer group. Control individuals (n = 43, matched for age with the Alzheimer group) displayed both plaques and tangles. In this subgroup neither plaques nor tangles correlated with age; however, there was a significant correlation betwen senile plaques and neurofibrillary tangles. We hypothesize that the continuous activity of underlying processes associated with senile plaques and neurofibrillary tangles formation or resolution might lead to the unbalanced production of these lesions in Alzheimer's disease.