No correlation between nigral degeneration and striatal plaques in Alzheimer's disease

Although Alzheimer's disease may involve both the substantia nigra and the striatum, there is little information concerning the relationship between the resulting abnormalities in these reciprocally interconnected regions of the brain. We have examined the correlation between plaque density in the striatum and counts of neurons and neurofibrillary tangles in the pars compacta of the substantia nigra, in 12 cases of "pure" Alzheimer's disease (i.e. without clinical or neuropathological evidence of Parkinson's or cortical Lewy body disease) and 11 normal controls. Diffuse plaques in the striatum and neurofibrillary tangles in the substantia nigra were consistent findings in all of the Alzheimer brains. However, quantitation did not reveal a statistically significant correlation between the density of striatal plaques and the numbers of either neurofibrillary tangles or neurons in the substantia nigra. Although the mean number of neurons in the substantia nigra of Alzheimer brains was lower than that in controls, the difference did not reach statistical significance. We suggest that previous assessments of substantial loss of nigral neurons in Alzheimer's disease may have been skewed by the inclusion of cases with coexistent cortical Lewy bodies.