Neuropathologic Classification of Dementias: Introduction

Publisher Summary This chapter describes that the neuropathology of dementia may appear at present as a “science of inclusion bodies.” This nosology of microscopic events is sometimes said to lack a unifying synthesis. The study of the degenerative dementias tends indeed to show that there is not a unique mechanism of neurodegeneration but a myriad of different and probably often unconnected processes that can contribute to the cognitive defect. The neuropathologist, like the neurologist, relies on two types of information to make the diagnosis of a dementing disorder: the topography and the nature of the lesions. The topography determines which clinical symptoms are present, whereas the nature of the lesions determines the progression of the symptoms. Strongly based on the anatomy of the neuronal loss, the neuropathology of degenerative diseases now depends mainly on the identification of inclusion bodies whose nature is probed by immunohistochemistry. Loss of neurons and of synapses and astrocytosis are unspecific lesions; neuronal chromatolysis is observed in a few disorders, but the accumulations of proteins in the cells or in the extracellular space are currently considered the most specific signs.