Pathology in primary progressive aphasia syndromes.

'Primary progressive aphasia' (PPA) refers to core linguistic disorders caused by neurodegenerative disease. Three main PPA variants are recognized: nonfluent/agrammatic, semantic and logopenic. Correctly classifying patients during life according to the underlying histopathology will become increasingly important as cause-specific treatments become available. This article reviews clinical and histopathological studies of PPA, with particular reference to updated PPA classifications. Currently, one-to-one relationships do not exist within PPA subtypes. The semantic variant has the best correspondence between the clinical syndrome and the underlying pathological cause and the logopenic variant the worst correspondence. The use of future biomarkers should facilitate accurate clinicopathological correlation of patients during life.