Primary progressive aphasia and Alzheimer's disease: brief history, recent evidence.

Primary progressive aphasia (PPA) has been recognized as a syndrome distinct from the usual pattern of language deterioration in Alzheimer's disease and typically more related to the pathology of frontotemporal dementia (FTD). In recent years, however, the syndromes of primary progressive aphasia have become more complex, divided into the three subtypes of progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopenic/phonological progressive aphasia (LPA). These syndromes have not only made the linguistic analysis more complex, but the associated pathologies have also become more variable. In particular, PNFA is usually, but not always, associated with FTD pathology and often evidence of a tau mutation, but rarely AD; SD is usually associated with FTD of the ubiquitin staining or progranulin (TAR-DNA) mutation type, but, again, occasionally AD; LPA is typically associated with AD pathology. Patterns of atrophy on magnetic resonance imaging (MRI) generally conform to these subtypes, with PNFA associated with left frontal and insular atophy, SD associated with bilateral temporal atrophy, and LPA associated with L superior-posterior temporal and parietal atrophy. These patterns can also be seen on positron emission (PET) scanning with fluorodeoxyglucose. The newer amyloid binding ligand PET technologies are less useful for detecting regional atrophy patterns but more useful for indication of the underlying pathology. We can thus speak of syndromes of PPA or underlying pathological bases of PPA.