An Overview of Primary Dementias as Clinicopathological Entities

Dementia is a state of cognitive dysfunction which leads to functional decline. It is a syndrome caused by several medical and neurological causes, but most cases of dementia are due to "primary dementias." Primary dementias are neurological diseases whose manifestations are predominantly cognitive. Most primary dementias are caused by neurodegenerative proteinopathies where an accumulation of misfolded proteins leads to neuronal loss, neuroinflammation and glial reaction. Each proteinopathy is characterized by the type of protein implicated in its pathophysiology. Neurodegenerative dementias include the most prevalent cause of dementia-Alzheimer's disease-as well as Lewy body dementia, Parkinson's disease dementia, frontotemporal dementias, and prion diseases. Vascular dementia, especially small vessel disease, though not a neurodegenerative condition, is often grouped together with primary dementias. Each type of proteinopathy, characterized by the location and nature of misfolded protein accumulation, may correspond to a particular clinical phenotype. The correspondence between pathologies and clinical phenotypes is not exclusive, and there is a large degree of overlap. Although in the research setting the clinicopathological construct is on the wane, in the clinic it is the most practical way of approaching primary dementias. In this article, we introduce the clinicopathological construct, the understanding of which will form the basis of the other articles in this volume.