Histopathology of the substantia nigra in Alzheimer's disease

Histopathologic examination of the pars compacta of the substantia nigra of 17 patients with Alzheimer's disease showed Lewy bodies in six, neurofibrillary tangles in another six and only histologic changes that did not differ from age-matched controls in five patients. Four of the six patients with nigral Lewy bodies showed severe loss of neural cell bodies, reactive astrocytosis, gliosis and neuromelanin in macrophages and in the neuropile. By contrast, the loss of neuronal cell bodies in our patients without nigral Lewy bodies regardless of whether or not they also had nigral neurofibrillary tangles was no greater than what we observed in our age-matched controls. Quantitative cell counts confirmed our histopathologic estimates of neuronal loss. Our study and the findings of others show that the substantia nigra is often abnormal in Alzheimer's disease and that the abnormalities are rarely severe without nigral Lewy bodies.