Morphometric investigation of nerve cells, neuropil and senile plaques in senile dementia of the Alzheimer type.

Eight brains from patients with a mean age of 82 years showing clinical and neuropathological manifestations of senile dementia of the Alzheimer type (SDAT) and 6 control brains from individuals with a mean age of 89 years who were mentally normal or who had minimal senile impairment of memory, were selected by a rigorous elimination procedure for final evaluation from a total of 26 brains. Using an optical electronic image-analysis system, stereological measurements were made of the size and number of senile plaques, and of nerve cell area, capillary diameter, capillary length and intercapillary distance in the medial frontal gyrus, medial temporal gyrus and precentral gyrus. The number and size of senile plaques did not correlate with any of the other parameters measured, whereas Mountjoy et al. (1983) found a correlation between neuronal count and plaque count. In SDAT the cerebral cortex displayed significant atrophy of the neuronal perikarya (mean decrease approximately 50%). The greatest decrease in nerve cell area (55%) was seen in layers III and IV of the medial temporal cortex. Stereological measurements on the capillary network revealed only moderate neuropil shrinkage. Capillary volume was on average 30% greater in SDAT as a result of a decrease in intercapillary distance. These findings indicate that nerve cell shrinkage is a characteristic indicator of senile dementia. Neuropil atrophy may be of secondary importance.