Focal cortical atrophy syndromes.

The topography of Alzheimer's disease (AD) and its effects on language, perception, and praxis are briefly reviewed as background to the focal cortical atrophy syndromes, including primary progressive aphasia (PPA), posterior cortical atrophy (PCA), and corticobasal degeneration (CBD). Simplistically speaking, there are two main pathological and neuroimaging phenotypes associated with these syndromes. One is frontotemporal degeneration (FTD), a nonspecific spongiform degeneration, with gliosis and neuronal loss, sometimes with Pick cells and bodies, which is usually selective for frontal and anterior temporal cortex. The other is Alzheimer's disease, in which amyloid plaques and neurofibrillary tangles initially develop in the hippocampal region, and spread to the lateral temporal and parietal neocortex and then to the frontal cortex. In the case of PPA, left perisylvian dysfunction is usually evident at presentation clinically and on neuroimaging. Nonfluent progressive aphasia tends to progress anteriorly and is usually associated with FTD. In fluent progressive aphasia, the pathology may progress anteriorly due to FTD or posteriorly, reflecting AD. In PCA, the visual association cortex is targeted bilaterally, often more so on the right, and the pathology is usually indicative of AD. CBD is an asymmetric akinetic-rigid syndrome associated with apraxia, in which swollen achromatic neurons are present in the frontoparietal cortex and substantia nigra on light microscopy, suggesting to some that it may fall within the spectrum of FTD and Pick's disease. The application of new molecular biological techniques, however, suggest that CBD, FTD, and Pick's Disease may be pathologically distinct. The clinico-pathological features of each syndrome are reviewed and compared to those typical for AD, and single photon emission computerized tomography scans representative for each are illustrated.