Is there a spatial association between senile plaques and neurofibrillary tangles in Alzheimer's disease?

Obective: To test the hypothesis that the clusters of senile plaques (SP) and neurofibrillary tangles (NFT) in patients with Alzheimer disease (AD) are spatially associated as predicted by the Amyloid Cascade Hypothesis'. Methods. The spatial association between the SP and NFT was studied in the cerebral cortex and hippocampus in six cases of sporadic Alzheimer disease (AD) using contingency tables. The coefficient C-7 Was used as an index of spatial association while chi-square with correction for continuity was used as a test of significance. Results. In the brain regions analysed, values of C7 were in the range -0.31 to +032 but a statistically significant spatial association between SP and NFT was present in only 8/39 (21%.) regions. The degree of spatial association between the SP and NFT was similar in different brain regions and did not vary with apolipoprotein c genotype of the patient. However the magnitude of C-7 in a region was positively correlated with the density of the NFT and with the total density of SP and NFT but not with the density of SP alone. Conclusion: There was little evidence that SP and NFT were spatially associated except in brain areas with high densities of lesions. The data support the hypothesis that SP and NFT are distributed relatively independently in the cerebral cortex and hippocampus and therefore, could be distinct phenomena in AD.