Chapter 20 Neuropathological hallmarks of Alzheimer's and Parkinson's diseases

Abstract

Alzheimer's disease and Parkinson's (Lewy body) disease, the most widespread degenerative illnesses of the human brain, involve multiple neuronal systems and are the consequences of changes in the neuronal cytoskeleton, which develop in only a few susceptible types of nerve cells. In Alzheimer's disease, affected neurons produce neurofibrillary tangles and neuropil threads, while in Parkinson's disease they develop Lewy bodies and Lewy neurites. In both illnesses a specific pattern of lesions evolves slowly over time and remains remarkably consistent across cases. In Alzheimer's disease, six developmental stages can be distinguished, reflecting the predictable manner in which the neurofibrillary changes spread through the telencephalic cortex. In stages I and II, the pathological process makes inroads into the transentorhinal and entorhinal regions; thereafter, in stages III and IV, it proceeds into the adjoining cortical and subcortical components of the limbic system. Eventually, in stages V and VI, the devastation engulfs association areas of the neocortex. In Parkinson's disease lesions also impair portions of the limbic system. The predilection sites include the transentorhinal and entorhinal regions, the CA2 sector of the Ammon's horn, the limbic thalamic nuclei, the anterior cingulated areas, agranular insular cortex, and components of the amygdala. In addition, non-thalamic nuclei with diffuse projections to the telencephalic cortex and centres that regulate endocrine and autonomic functions exhibit severe lesions.