Progression of Alzheimer histopathological changes

Area of Science:

• Neuropathology
• Geriatric Medicine
• Neurodegenerative Diseases

Background:

• Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs).
• Understanding the clinical-pathological correlations of AD in the elderly is crucial for diagnosis and treatment.
• Previous studies have explored these correlations, but specific patterns in older populations require further investigation.

Purpose of the Study:

• To investigate the relationship between neuropathological findings (Aβ deposits, NFTs, neuronal loss) and cognitive status in patients aged over 75.
• To determine the distribution patterns and chronological order of lesion development in different brain regions.
• To examine the correlation between specific pathological markers and the severity of intellectual deficit.

Main Methods:

• Prospective collection of clinical and pathological data from 31 elderly patients (>75 years) with varying degrees of Alzheimer disease.
• Pathological assessment included evaluation of Aβ peptide deposit density, neurofibrillary tangle distribution and density, and neuronal counts.
• Immunohistochemistry was used to detect SNAP-25 immunoreactivity, indicating axonal transport deficits.

Main Results:

• Aβ peptide deposit density showed a weak correlation with intellectual status; one patient with high Aβ density was cognitively normal.
• Aβ deposits were widespread in cortical samples, while limbic areas were often devoid of deposits.
• Neurofibrillary tangles exhibited a selective distribution, sparing primary cortical areas in milder cases and affecting associative cortices in intermediate cases. Hippocampal-parahippocampal areas were affected in all cases.
• NFT density correlated linearly with intellectual deficit in the hippocampus but stepwise in isocortical samples, suggesting a later involvement of isocortex.
• Severe neuronal loss in the supramarginal gyrus was observed only in the most affected cases with high NFT density (>5/mm²).
• Accumulation of SNAP-25 immunoreactivity indicated axonal transport deficits in severe AD cases.

Conclusions:

• The distribution pattern of NFTs suggests a chronological progression from limbic to associative and then to primary cortical areas.
• NFTs in the hippocampus are a strong predictor of intellectual decline in the elderly.
• Axonal transport deficits may contribute to neuronal loss in advanced stages of Alzheimer disease.