To stage, or not to stage.

Staging of neurodegenerative diseases is based chiefly on the topographical or anatomical extent of aggregated proteinaceous inclusions, and the density or severity of the lesions in a given region is usually assessed semiquantitatively. Associated phenomena, such as cell loss and synapse loss, are evaluated but not staged. This article reviews the development of neuropathological staging of the sporadic Alzheimer's and sporadic Parkinson's diseases. It considers challenges for staging systems, and it poses the question whether neuropathological staging as practiced up to now is still relevant.